structural insights into new bi(iii) coordination polymers

International Journal of

Molecular Sciences

Article

Structural Insights into New Bi(III) CoordinationPolymers with Pyridine-2,3-Dicarboxylic Acid:Photoluminescence Properties and Anti-Helicobacterpylori Activity

Mateusz Kowalik 1,* , Joanna Masternak 1 , Iwona Łakomska 2,* ,Katarzyna Kazimierczuk 3 , Anna Zawilak-Pawlik 4 , Piotr Szczepanowski 4,Oleksiy V. Khavryuchenko 5 and Barbara Barszcz 1

1 Institute of Chemistry, Jan Kochanowski University in Kielce, Uniwersytecka 7, 25-406 Kielce, Poland;[email protected] (J.M.); [email protected] (B.B.)

2 Faculty of Chemistry, Nicolaus Copernicus University in Torun, Gagarina 7, 87-100 Torun, Poland3 Department of Inorganic Chemistry, Faculty of Chemistry, Gdansk University of Technology,

G. Narutowicza 11/12, 80-233 Gdansk, Poland; [email protected] Laboratory of Molecular Biology of Microorganisms, Microbiology Department,

Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences,Weigla 12, 53-114 Wrocław, Poland; [email protected] (A.Z.-P.);[email protected] (P.S.)

5 Shupyk National Medical Academy of Postgraduate Education (NMAPE),Dorogozhytska 9, 04112 Kyiv, Ukraine; [email protected]

* Correspondence: [email protected] (M.K.); [email protected] (I.Ł.);Tel.: +48-56-611-4510 (I.Ł.)

Received: 15 October 2020; Accepted: 17 November 2020; Published: 18 November 2020 ��

Abstract: Two novel coordination polymers, [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1) and {(Et3NH)2

[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2) were prepared using as a prolinker pyridine-2,3-dicarboxylic acid(2,3pydcH2). The obtained complexes were fully characterized by elemental analysis, TG/DTG, FT-IR,solid-state photoluminescence, DFT calculations and single-crystal X-ray diffraction. The obtainedcomplexes crystallized in the triclinic P-1 space group (1) and comprise dimeric units with twocrystallographically different Bi(III) centers (polyhedra: distorted pentagonal bipyramid andbicapped trigonal prism) and monoclinic P21/c space group (2) with a distorted monocappedpentagonal bipyramid of Bi(III) center. The various coordination modes of bridging carboxylateligands are responsible for the formation of 1D chains with 4,5C10 (1) and 2C1 (2) topology.The photoluminescence quantum yield for polymer 2 is 8.36%, which makes it a good candidate formore specific studies towards Bi-based fluorescent materials. Moreover, it was detected that polymer1 is more than twice as active against H. pylori as polymer 2. It can be concluded that there is anexisting relationship between the structure and the antibacterial activity because the presence ofchloride and triethylammonium ions in the structure of complex 2 reduces the antibacterial activity.

Keywords: Bi(III) coordination polymers; pyridine-2,3-dicarboxylic acid; holodirected and hemidirectedgeometry; photoluminescence; Helicobacter pylori

1. Introduction

Contemporary coordination chemistry establishes a scientific basis for obtaining compounds usedas sources for synthesizing functional materials not only for technology [1–7] but also for medicine orpharmacy [8,9]. It is a great challenge to obtain proper functional materials because the properties of

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coordination compounds depend on the type of both metal ions and connecting ligands. Our interestin this field concerns the chemistry of lead(II) [10–14] and bismuth(III) coordination polymers withheteroaromatic carboxylate ligands. When selecting a central ion, we focused on the multipleapplications of Bi(III) compounds as, for example, photoluminescent materials [15–17], catalysts [18],medical drugs for gastrointestinal disorders caused by Helicobacter pylori or anticancer agents [19–22].Furthermore, the Bi(III) ion exhibits a [Xe]4f 145d106s2 ground state electronic configuration andbelongs to a group of metal ions (Tl(I), Pb(II), Sn(II), Sb(III)) possessing a lone electron pair (ns2).The presence of a lone electron pair, its stereochemical role and a relatively large bismuth covalentradius (1.48 Å [23]) can lead to the formation of interesting molecular structures of Bi-based complexes,including high coordination numbers and a hemi- or holodirected distribution of ligands aroundthe metal center. When the lone electron pair is stereochemically inactive, it does not affect thegeometry of the metal coordination environment. The bonds between metal and ligands are distributedsymmetrically and the geometry around the central ion is defined as holodirected. While when theelectron pair is stereochemically active, it occurs in a separate place in the central ion environment.The coordination bonds are distributed asymmetrically and only in a certain part of the coordinationsphere. Such a type of geometry is called hemidirected [24]. These features make Bi(III) a coordinativelyflexible ion, which is why we chose it for the synthesis of novel bismuth(III) coordination polymers.Additionally, the varied coordination structures of bismuth(III) complexes are also affected by thekind of donating ligand and the different coordination modes. This is especially important in thesynthesis of functional coordination polymers (CPs), where ligands play an additional role as organiclinkers. Among these linkers, carboxylate ligands are special, mainly due to the large variation intheir coordination behavior. They can act as (i) monodentate κO, (ii) chelating κ2O,O′, (iii) bridgingµ-κO:κO′, µ-κO:κO, µ3-κO:κO′:κO′, µ4-κO:κO:κO′:κO′ and (iv) chelating-bridging µ-κ2O,O′:κO′,µ3-κO:κ2O,O′:κO′, µ4-κO:κ2O,O′:κO′:κO′, µ5-κO:κO:κ2O,O′:κO′:κO′ ligands [25]. When researchingexamples of functional bismuth(III) coordination polymers in the literature, we focused on complexeswith isomeric pyridine-dicarboxylic acids as linkers: pyridine-2,3-dicarboxylic acid (2,3pydcH2) [26],pyridine-2,5-dicarboxylic acid (2,5pydcH2) [27–31], pyridine-2,6-dicarboxylic acid (2,6pydcH2) [32–37],pyridine-3,4-dicarboxylic acid (3,4pydcH2) [37] and pyridine-3,5-dicarboxylic acid (3,5pydcH2) [38].A literature search of coordination polymer functionality revealed six examples of Bi(III) complexeswith luminescence properties [27,28,31,32,38]; three compounds exhibited gas-sorption behavior(CO2, N2, H2) [32], and one was used as a precursor for the preparation of Bi2O3 nanoparticles viathermal decomposition [26]. However, the biological activity of the mentioned complexes have notbeen examined, although all of the bismuth compounds clinically used against Helicobacter pyloribelong to a group of Bi(III) carboxylates (bismuth subsalicylate (BSS, Pepto-Bismol), colloidal bismuthsubcitrate (CBS, De-Nol) or ranitidine bismuth citrate (RBC, Pylorid)) [39,40]. Currently, the problemsassociated with this microaerophilic and neutralophilic Gram negative bacterium have been intensivelyinvestigated because it has been linked not only to many gastrointestinal disorders but also to gastriccancer. It should be noted that bismuth medications have been used not only against H. pylori as acomponent of quadruple therapies [41] as the first-line treatment (two antibiotics, proton-pump inhibitorand Bi-based drug), but Bi(III) complexes have also demonstrated anticancer activity. Additionally,bismuth was employed in radiation therapy in the form of Bi-nanoparticles and nanodots or intargeted radioimmunotherapy in the form of bismuth radionuclides [42]. Considering all of the aboveaspects of interesting bismuth chemistry, herein, we present the synthesis and characterization of newBi(III) metal-organic coordination polymers. Taking into consideration our previous experience in theconstruction of CPs based on Pb(II) ions [10–14], we paid special attention to the choice of a properorganic linker. We selected pyridine-2,3-dicarboxylic acid as the prolinker for this purpose. It belongsto the group of multidonating N,O-donor ligands, which can exist in a mono- or a fully deprotonatedform, indicating the possibility of different coordination modes with metal ions [43–55] (Scheme 1).

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Scheme 1. Selected coordination modes of mono-deprotonated-2,3pydcH (top) and deprotonated-2,3pydc (bottom) forms of pyridine-2,3-dicarboxylic acid (2,3pydcH2) in coordination with different metal ions reported in the literature [43–55].

During the course of this study, we (i) synthesized and fully physicochemically characterized two novel bismuth(III) coordination polymers with pyridine-2,3-dicarboxylic acid (2,3pydcH2) as a prolinker; (ii) presented the molecular structure and topology of [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1) and {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2); (iii) confirmed and visualized the intermolecular close contacts in the crystal structures; (iv) carried out DFT (density functional theory) calculations to provide an explanation for the lone pair activity; (v) studied the luminescence properties of the obtained coordination polymers in the solid-state; and (vi) determined the bacteriostatic activity against H. pylori, which was compared with other Bi(III) carboxylate complexes.

2. Results and Discussion

2.1. Molecular Structure and Lone Pair Stereoactivity

The SC-XRD studies revealed that the coordination polymer [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1) crystallized in the triclinic space group P-1. The asymmetric unit contained dimeric units of two crystallographically distinguishable Bi(III) centers. There were two anions of pyridine-2,3-dicarboxylic acid for each Bi center, one deprotonated (2,3pydc) and one mono-deprotonated (2,3pydcH). Additionally, there was one water molecule coordinated to the Bi1 center (Figure 1a). Each metal center existed in a different coordination environment. Around the Bi1 atom, there was a structural gap between the N2, O7 and O15 donor atoms, suggesting the influence of the lone electron pair on the geometry of the coordination sphere. The coordination bonds with those atoms were significantly longer (2.521–2.710 Å) than those with the other atoms (O5, O1 and N1, 2.314–2.386 Å) and were located opposite to the location of the lone electron pair (Table 1). Taking into consideration only the mentioned strong bonds, the geometry of the nearest coordination environment of the Bi1 center exhibited a coordination number of 7 and could be described as hemidirected. However, due to the significant stereoactivity of the lone electron pair, there were two additional donor atoms (O8

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Scheme 1. Selected coordination modes of mono-deprotonated-2,3pydcH (top) and deprotonated-2,3pydc (bottom) forms of pyridine-2,3-dicarboxylic acid (2,3pydcH2) in coordination with differentmetal ions reported in the literature [43–55].

During the course of this study, we (i) synthesized and fully physicochemically characterizedtwo novel bismuth(III) coordination polymers with pyridine-2,3-dicarboxylic acid (2,3pydcH2) as aprolinker; (ii) presented the molecular structure and topology of [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n

(1) and {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2); (iii) confirmed and visualized the intermolecularclose contacts in the crystal structures; (iv) carried out DFT (density functional theory) calculationsto provide an explanation for the lone pair activity; (v) studied the luminescence properties of theobtained coordination polymers in the solid-state; and (vi) determined the bacteriostatic activity againstH. pylori, which was compared with other Bi(III) carboxylate complexes.

2. Results and Discussion

2.1. Molecular Structure and Lone Pair Stereoactivity

The SC-XRD studies revealed that the coordination polymer [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n

(1) crystallized in the triclinic space group P-1. The asymmetric unit contained dimeric units of twocrystallographically distinguishable Bi(III) centers. There were two anions of pyridine-2,3-dicarboxylicacid for each Bi center, one deprotonated (2,3pydc) and one mono-deprotonated (2,3pydcH).Additionally, there was one water molecule coordinated to the Bi1 center (Figure 1a). Each metalcenter existed in a different coordination environment. Around the Bi1 atom, there was a structuralgap between the N2, O7 and O15 donor atoms, suggesting the influence of the lone electron pair onthe geometry of the coordination sphere. The coordination bonds with those atoms were significantlylonger (2.521–2.710 Å) than those with the other atoms (O5, O1 and N1, 2.314–2.386 Å) and werelocated opposite to the location of the lone electron pair (Table 1). Taking into consideration onlythe mentioned strong bonds, the geometry of the nearest coordination environment of the Bi1 centerexhibited a coordination number of 7 and could be described as hemidirected. However, due to thesignificant stereoactivity of the lone electron pair, there were two additional donor atoms (O8 and O17)which were more distant from the Bi1 center (2.829 and 2.841 Å, respectively). These atoms, connected

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by weaker secondary bonds, completed the Bi1 coordination sphere. Therefore, the coordinationnumber increased to 9, and the Bi1 coordination environment resembled a holodirected geometry [24].The difference between the longest and shortest coordination bonds was 0.527 Å, which indicateda significant distortion of the coordination polyhedron. The Bi2 center was surrounded by eightdonor atoms connected by strong primary bonds (2.311–2.650 Å) and one atom (O16) connected at adistance of 2.842 Å (secondary bond). In this case, the geometry of the Bi2 center was determined ashemidirected for CN = 8 or holodirected for CN = 9 [24].

It is important to confirm the conclusions drawn from the crystallographic analysis by DFTcalculations. One of the crucial factors affecting the lone electron pair stereoactivity is the type oforbital, i.e., a spherical s orbital or space-oriented p or d orbitals, in which the electron density ismainly localized. Concerning compound 1, the stereoactivity of the lone electron pair was slightlymore pronounced in the Bi1 center than in Bi2 (Figure 1b). The localization of the lone electron pair inthe Bi1 center indicated a significant contribution of the p orbital (35.3%) and a smaller contributionof the s orbital (9.5%). This caused the electron density to occupy a hemisphere in close proximityto the metal center. As a result, there was a gap in the structure, and the surrounding Bi1 atomadopted a hemidirected geometry. The lone pair stereoactivity in the Bi1 center caused the distortionof the coordination environment but simultaneously allowed for the formation of two additionalcoordination bonds with atoms located at a distance >2.8 Å. Therefore, the coordination geometrywas not a typical hemidirected geometry since including secondary bonds filled up the hemisphere,resulting in a holodirected geometry. In turn, there was a smaller contribution of the p orbital (30.2%)and a slightly greater contribution of the s orbital (12.0%) in the localization of the electron pair inthe Bi2 center than in the Bi1 center. As a result, the electron density in the Bi2 center affected thedistortion of the coordination environment to a lower extent, and there was only one atom connectedwith the metal center by a secondary bond. However, concerning only primary bonds, the geometry ofBi2 was hemidirected, while including secondary bonds resulted in a holodirected geometry.

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and O17) which were more distant from the Bi1 center (2.829 and 2.841 Å, respectively). These atoms, connected by weaker secondary bonds, completed the Bi1 coordination sphere. Therefore, the coordination number increased to 9, and the Bi1 coordination environment resembled a holodirected geometry [24]. The difference between the longest and shortest coordination bonds was 0.527 Å, which indicated a significant distortion of the coordination polyhedron. The Bi2 center was surrounded by eight donor atoms connected by strong primary bonds (2.311–2.650 Å) and one atom (O16) connected at a distance of 2.842 Å (secondary bond). In this case, the geometry of the Bi2 center was determined as hemidirected for CN = 8 or holodirected for CN = 9 [24].

It is important to confirm the conclusions drawn from the crystallographic analysis by DFT calculations. One of the crucial factors affecting the lone electron pair stereoactivity is the type of orbital, i.e., a spherical s orbital or space-oriented p or d orbitals, in which the electron density is mainly localized. Concerning compound 1, the stereoactivity of the lone electron pair was slightly more pronounced in the Bi1 center than in Bi2 (Figure 1b). The localization of the lone electron pair in the Bi1 center indicated a significant contribution of the p orbital (35.3%) and a smaller contribution of the s orbital (9.5%). This caused the electron density to occupy a hemisphere in close proximity to the metal center. As a result, there was a gap in the structure, and the surrounding Bi1 atom adopted a hemidirected geometry. The lone pair stereoactivity in the Bi1 center caused the distortion of the coordination environment but simultaneously allowed for the formation of two additional coordination bonds with atoms located at a distance >2.8 Å. Therefore, the coordination geometry was not a typical hemidirected geometry since including secondary bonds filled up the hemisphere, resulting in a holodirected geometry. In turn, there was a smaller contribution of the p orbital (30.2%) and a slightly greater contribution of the s orbital (12.0%) in the localization of the electron pair in the Bi2 center than in the Bi1 center. As a result, the electron density in the Bi2 center affected the distortion of the coordination environment to a lower extent, and there was only one atom connected with the metal center by a secondary bond. However, concerning only primary bonds, the geometry of Bi2 was hemidirected, while including secondary bonds resulted in a holodirected geometry.

(a) (b)

Figure 1. (a) The molecular structure with an atom numbering scheme of complex 1 (Symmetry codes: (i) −x, 1 − y, 1 − z; (ii) 1 − x, 1 − y, 1 − z) (Bi—orange, O—red, N—blue, C—black, H—white); (b)

Figure 1. (a) The molecular structure with an atom numbering scheme of complex 1 (Symmetry codes:(i)−x, 1− y, 1− z; (ii) 1− x, 1− y, 1− z) (Bi—orange, O—red, N—blue, C—black, H—white); (b) graphicalrepresentation of selected molecular orbital localized on Bi atom in complex 1 (DFT calculations).

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Table 1. Selected bond lengths (Å) and angles (◦) for complex 1.

Bond Lengths (Å)

Bi1–O5 2.314(10) Bi1–O7 2.697(9) Bi2–O9 2.311(9) Bi2–O14 ii 2.539(9)Bi1–O1 2.332(9) Bi1–O15 2.710(9) Bi2–O15 2.433(9) Bi2–N4 2.640(11)Bi1–N1 2.386(12) Bi1–O8 2.829(10) Bi2–O8 2.484(10) Bi2–O14 2.650(10)Bi1–O13 2.443(9) Bi1–O17 2.841(10) Bi2–O6 i 2.491(9) Bi2–O16 2.842(10)Bi1–N2 2.521(12) Bi2–N3 2.506(10)

Bond Angles (◦)

O1–Bi1–N2 74.3(4) O5–Bi1–O7 141.6(3) O15–Bi2–N3 117.4(4)O1–Bi1–N1 68.8(4) O5–Bi1–O17 121.4(3) O15–Bi2–N4 141.6(3)O1–Bi1–O5 131.9(3) O13–Bi1–O15 72.8(3) O15–Bi2–O9 77.2(3)O1–Bi1–O13 135.0(3) O13–Bi1–O8 88.2(3) O14–Bi2–O16 117.2(3)O1–Bi1–O15 143.0(3) O13–Bi1–O7 77.9(3) O14–Bi2–O6 i 70.4(3)O1–Bi1–O8 88.8(3) O13–Bi1–O17 140.9(3) O14–Bi2–O14 ii 71.6(3)O1–Bi1–O7 67.3(3) O15–Bi1–O8 65.0(3) O14–Bi2–N3 145.4(3)O1–Bi1–O17 71.9(3) O15–Bi1–O7 106.3(3) O14–Bi2–N4 111.2(3)N2–Bi1–N1 84.0(4) O15–Bi1–O17 72.6(3) O14–Bi2–O9 144.6(3)N2–Bi1–O5 66.1(3) O8–Bi1–O7 47.9(3) O16–Bi2–O6 i 79.4(3)

N2–Bi1–O13 130.9(3) O8–Bi1–O17 60.9(3) O16–Bi2–O14 ii 138.5(3)N2–Bi1–O15 107.2(3) O7–Bi1–O17 95.0(3) O16–Bi2–N3 69.3(4)N2–Bi1–O8 137.8(3) O8–Bi2–O15 74.5(3) O16–Bi2–N4 131.2(3)N2–Bi1–O7 141.2(3) O8–Bi2–O14 72.2(3) O16–Bi2–O9 65.1(3)

N2–Bi1–O17 77.1(4) O8–Bi2–O16 115.1(3) O6 i–Bi2–O14 ii 65.4(3)N1–Bi1–O5 80.6(4) O8–Bi2–O6 i 142.4(3) O6 i–Bi2–N4 78.3(4)

N1–Bi1–O13 77.0(4) O8–Bi2–O14 ii 106.2(3) O6 i–Bi2–N4 122.8(3)N1–Bi1–O15 147.6(3) O8–Bi2–N3 138.0(6) O6 i–Bi2–O9 138.6(3)N1–Bi1–O8 126.0(4) O8–Bi2–N4 75.4(3) O14 ii–Bi2–N3 82.5(5)N1–Bi1–O7 78.1(4) O8–Bi2–O9 75.5(3) O14 ii–Bi2–N4 61.7(3)

N1–Bi1–O17 139.7(4) O15–Bi2–O14 80.7(3) O14 ii–Bi2–O9 132.0(3)O5–Bi1–O13 66.4(3) O15–Bi2–O16 48.6(3) N3–Bi2–N4 73.3(6)O5–Bi1–O15 76.8(3) O15–Bi2–O6 i 95.5(3) N3–Bi2–O9 69.2(6)O5–Bi1–O8 139.1(3) O15–Bi2–O14 ii 150.7(3) N4–Bi2–O9 73.3(3)

Symmetry codes: i−x, 1 − y, 1 − z; ii 1 − x, 1 − y, 1 − z.

Coordination polymer {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2) crystallized in the monoclinicspace group P21/c. Its asymmetric unit comprised one Bi(III) ion, one molecule of pyridine-2,3-dicarboxylato ligand (2,3pydc), one molecule of 3-carboxypyridine-2-carboxylato ligand (2,3pydcH)and two coordinated chloride ions. Compound 2 is an anionic polymer, and the negative chargeis neutralized by two triethylammonium cations for each Bi(III) center (Figure 2a). In contrast tocomplex 1, the donor atoms in complex 2 were connected with the metal center only by primary bonds(CN = 8), which range from 2.374 to 2.725 Å (Table 2). The chromophore was formed as {BiO4N2Cl2}.The difference in the coordination bond lengths (0.351 Å) and angles slightly distorted the structure ofthe coordination environment from an ideal monocapped pentagonal bipyramid. However, a lack ofobvious gaps and secondary bonds in the proximity of the Bi(III) center suggested that the lone electronpair was stereochemically inactive or weakly active and did not significantly affect the structure.Consequently, the nearest coordination environment of the Bi(III) center in compound 2 exhibited aholodirected geometry [24].

Additionally, the DFT calculations indicated the conclusion from structural studies. There was asmaller contribution of the p orbital (29.2%) and a slightly larger contribution of the s orbital (14.6%)to the localization of the lone electron pair in the Bi(III) center of compound 2 (Figure 2b) comparedwith the Bi(III) centers of compound 1. As a result, the electron density was more centered andinsignificantly influenced the structure distortion.

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with the Bi(III) centers of compound 1. As a result, the electron density was more centered and insignificantly influenced the structure distortion.

(a) (b)

Figure 2. (a) The molecular structure with an atom numbering scheme of complex 2 (Symmetry code: (i) x, 0.5 − y, −0.5 + z) (Bi—orange, O—red, N—blue, Cl— green, C—black, H—white); (b) graphical representation of selected molecular orbital localized on Bi atom in complex 2 (DFT calculations).

Table 2. Selected bond lengths (Å) and angles (°) for complex 2.

Bond Lengths (Å) Bi1–O5 2.374(7) Bi1–N1 2.546(7) Bi1–O7 i 2.651(6) Bi1–O8 i 2.721(7) Bi1–O1 2.429(7) Bi1–N11 2.585(7) Bi1–Cl2 2.672(2) Bi1–Cl1 2.725(3)

Bond Angles (°) O1–Bi1–N1 65.5(2) N1–Bi1–N11 140.9(2) O5–Bi1–O7 i 136.5(2) O1–Bi1–Cl1 97.3(3) N1–Bi1–O7 i 138.2(2) O5–Bi1–Cl2 83.6(8) O1–Bi1–O5 140.5(2) N1–Bi1–Cl2 82.8(5) O8 i–Bi1–N11 81.3(2) O1–Bi1–O8 i 77.5(2) Cl1–Bi1–O5 83.5(3) O8 i–Bi1–O7 i 48.4(2) O1–Bi1–N11 153.5(2) Cl1–Bi1–O8 i 74.3(2) O8 i–Bi1–Cl2 125.8(5) O1–Bi1–O7 i 75.2(2) Cl1–Bi1–N11 92.0(2) N11–Bi1–O7 i 78.8(2) O1–Bi1–Cl2 82.3(10) Cl1–Bi1–O7 i 122.7(2) N11–Bi1–Cl2 97.6(9) N1–Bi1–Cl1 77.8(2) Cl1–Bi1–Cl2 158.8(3) O7 i–Bi1–Cl2 77.9(4) N1–Bi1–O5 76.3(2) O5–Bi1–O8 i 138.8(2) N1–Bi1–O8 i 129.7(2) O5–Bi1–N11 65.1(2)

Symmetry code: i x, 0.5 − y, −0.5 + z.

2.2. Topology and Supramolecular Structure

In the structure of coordination polymer 1, the monoanionic ligand molecules (2,3pydcH) were connected to the metal center via a chelating (κ2N,O) coordination. In turn, dianionic ligand molecules (2,3pydc) exhibit two kinds of chelating-bridging coordination modes. One of them connects four metal centers according to µ4-κ2N,O:κO′:κO″:κ2O″,O‴, while the second one bridges five Bi(III) centers according to µ5-κ2N,O:κO:κO′:κO″:κ2O″,O‴ (Figure 3a). The water molecule acted as a monocoordinated ligand. Bridging ligand molecules were responsible for the formation of 1D chains along the a axis with a 4,5C10 topology described by the (45∙6)(49∙6) point symbol. This type of the underlying net is constructed by 4-connected [Bi1(2,3pydcH)(H2O)] and 5-connected [Bi2(2,3pydcH)] nodes linked together by 4- and 5-connected [2,3pydc] linkers (Figure 3b). The Bi∙∙∙Bi distances ranged from 4.196 to 8.879 Å. The relatively short Bi∙∙∙Bi separations (about 4.2 Å) are close

Figure 2. (a) The molecular structure with an atom numbering scheme of complex 2 (Symmetry code:(i) x, 0.5 − y, −0.5 + z) (Bi—orange, O—red, N—blue, Cl— green, C—black, H—white); (b) graphicalrepresentation of selected molecular orbital localized on Bi atom in complex 2 (DFT calculations).

Table 2. Selected bond lengths (Å) and angles (◦) for complex 2.

Bond Lengths (Å)

Bi1–O5 2.374(7) Bi1–N1 2.546(7) Bi1–O7 i 2.651(6) Bi1–O8 i 2.721(7)Bi1–O1 2.429(7) Bi1–N11 2.585(7) Bi1–Cl2 2.672(2) Bi1–Cl1 2.725(3)

Bond Angles (◦)

O1–Bi1–N1 65.5(2) N1–Bi1–N11 140.9(2) O5–Bi1–O7 i 136.5(2)O1–Bi1–Cl1 97.3(3) N1–Bi1–O7 i 138.2(2) O5–Bi1–Cl2 83.6(8)O1–Bi1–O5 140.5(2) N1–Bi1–Cl2 82.8(5) O8 i–Bi1–N11 81.3(2)

O1–Bi1–O8 i 77.5(2) Cl1–Bi1–O5 83.5(3) O8 i–Bi1–O7 i 48.4(2)O1–Bi1–N11 153.5(2) Cl1–Bi1–O8 i 74.3(2) O8 i–Bi1–Cl2 125.8(5)O1–Bi1–O7 i 75.2(2) Cl1–Bi1–N11 92.0(2) N11–Bi1–O7 i 78.8(2)O1–Bi1–Cl2 82.3(10) Cl1–Bi1–O7 i 122.7(2) N11–Bi1–Cl2 97.6(9)N1–Bi1–Cl1 77.8(2) Cl1–Bi1–Cl2 158.8(3) O7 i–Bi1–Cl2 77.9(4)N1–Bi1–O5 76.3(2) O5–Bi1–O8 i 138.8(2)

N1–Bi1–O8 i 129.7(2) O5–Bi1–N11 65.1(2)

Symmetry code: i x, 0.5 − y, −0.5 + z.

2.2. Topology and Supramolecular Structure

In the structure of coordination polymer 1, the monoanionic ligand molecules (2,3pydcH) wereconnected to the metal center via a chelating (κ2N,O) coordination. In turn, dianionic ligand molecules(2,3pydc) exhibit two kinds of chelating-bridging coordination modes. One of them connects fourmetal centers according to µ4-κ2N,O:κO′:κO′′:κ2O′′,O′′′, while the second one bridges five Bi(III)centers according to µ5-κ2N,O:κO:κO′:κO′′:κ2O′′,O′′′ (Figure 3a). The water molecule acted as amonocoordinated ligand. Bridging ligand molecules were responsible for the formation of 1D chainsalong the a axis with a 4,5C10 topology described by the (45

·6)(49·6) point symbol. This type of the

underlying net is constructed by 4-connected [Bi1(2,3pydcH)(H2O)] and 5-connected [Bi2(2,3pydcH)]nodes linked together by 4- and 5-connected [2,3pydc] linkers (Figure 3b). The Bi···Bi distances rangedfrom 4.196 to 8.879 Å. The relatively short Bi···Bi separations (about 4.2 Å) are close to the sum of thevan der Waals radii (4.14 Å [56]). However, in the structure of 1 the shortest Bi···Bi separations are those

Int. J. Mol. Sci. 2020, 21, 8696 7 of 26

associated with Bi2O2 dimeric units. They might be considered simply a consequence of the bridgingby O-donor carboxylate groups from 2,3pydc linkers and they are not indicative of a Bi···Bi bond [57].


to the sum of the van der Waals radii (4.14 Å [56]). However, in the structure of 1 the shortest Bi∙∙∙Bi separations are those associated with Bi2O2 dimeric units. They might be considered simply a consequence of the bridging by O-donor carboxylate groups from 2,3pydc linkers and they are not indicative of a Bi∙∙∙Bi bond [57].

Figure 3. (a) Coordination modes of carboxylate ligands in complex 1; (b) a fragment of the 1D crystal structure merged with 4,5C10 underlying net in valence-bonded MOFs standard representation for coordination polymer 1 (Bi—orange, O—red, N—blue, C—black, H—white).

The supramolecular structure of coordination polymer 1 was stabilized through conventional hydrogen bonding (O–H∙∙∙O) between water molecules and the carboxylate ligands or between the carboxylic groups of the 2,3pydcH molecules and the carboxylate groups of the 2,3pydc ligands with d(H∙∙∙O) distances ranging from 1.801 to 2.574 Å (Figure 4a). Nonconventional (C–H∙∙∙O) hydrogen bonds, both intramolecular (Figure 4b) and intermolecular (Figure 4d), also played an important role. Moreover, π-stacking interactions between pyridine rings were observed in the structure at a distance of 4.043 Å (Figure 4c). The details of the interactions in complex 1 are listed in Table 3.

Figure 3. (a) Coordination modes of carboxylate ligands in complex 1; (b) a fragment of the 1D crystalstructure merged with 4,5C10 underlying net in valence-bonded MOFs standard representation forcoordination polymer 1 (Bi—orange, O—red, N—blue, C—black, H—white).

The supramolecular structure of coordination polymer 1 was stabilized through conventionalhydrogen bonding (O–H···O) between water molecules and the carboxylate ligands or between thecarboxylic groups of the 2,3pydcH molecules and the carboxylate groups of the 2,3pydc ligands withd(H···O) distances ranging from 1.801 to 2.574 Å (Figure 4a). Nonconventional (C–H···O) hydrogenbonds, both intramolecular (Figure 4b) and intermolecular (Figure 4d), also played an important role.Moreover, π-stacking interactions between pyridine rings were observed in the structure at a distanceof 4.043 Å (Figure 4c). The details of the interactions in complex 1 are listed in Table 3.

In the structure of complex 2, ligand 2,3pydcH exhibited a chelating coordination mode (κ2N,O),while ligand 2,3pydc exhibited a chelating-bridging coordination mode (µ-κ2N,O:κ2O′′,O′′′) (Figure 5a).Compound 2 was a 1-dimensional coordination polymer forming a zig-zag pattern along the c axis.From the topological point of view, this type of connection is described as 2C1 in the valence-bondedMOFs standard representation. 2-Connected [Bi(2,3pydcH)Cl2] nodes were combined by 2-connected[2,3pydc] linkers at a distance of 8.909 Å. In the H-bonded MOFs standard representation, the topologyof complex 2 was changed. Taking into account the strong O4–H4A···O6ii hydrogen bonds formedbetween the –COOH group of the 2,3pydcH ligand and the –COO– group of the 2,3pydc ligand,the dimensionality increased to 2D (bc plane). Nodes and linkers became 3-connected, which resultedin the formation of a honeycomb-like hcb net described by the 63 point symbol (Figure 5b).

Int. J. Mol. Sci. 2020, 21, 8696 8 of 26Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 8 of 26

(a) (c)

(b) (d)

Figure 4. The geometry of noncovalent interactions in complex 1: (a) O–H∙∙∙O, (b) C–H∙∙∙O intramolecular, (c) π∙∙∙π and (d) C–H∙∙∙O intermolecular (translucent molecules belong to adjacent chains) (Bi—orange, O—red, N—blue, C—black, H—white).

Table 3. The geometry of noncovalent interactions in complex 1.

Hydrogen Bonds Donor–H···Acceptor D–H (Å) H···A (Å) D···A (Å) D–H···A (°)

O3–H3A∙∙∙O7 iii 0.84(1) 1.801(28) 2.625(37) 166.46(4) O12–H12A∙∙∙O1 iv 0.84(1) 2.550(41) 3.171(40) 131.65(5) O17–H17B∙∙∙O9 0.87(1) 2.574(14) 3.208(30) 130.56(4) C5–H5∙∙∙O16 i 0.95(1) 2.220(38) 3.140(51) 162.68(4)

C10–H10∙∙∙O16 i 0.95(1) 2.489(38) 3.310(47) 144.71(5) C12–H12∙∙∙O1 0.95(1) 2.542(41) 3.012(42) 110.73(4) C12–H12∙∙∙O17 0.95(1) 2.926(38) 3.409(51) 112.79(3)

C12–H12∙∙∙O12 A iv 0.95(1) 2.211(36) 2.957(53) 134.64(4) C17–H17∙∙∙O11 vi 0.95(2) 2.519(5) 3.313(13) 141.00(3)

C17–H17∙∙∙O11 A vi 0.95(2) 2.699(41) 3.278(36) 119.81(3) C18–H18∙∙∙O2 vii 0.95(2) 2.901(10) 3.496(23) 121.81(3) C19–H19∙∙∙O7 ii 0.95(1) 2.483(20) 3.346(22) 150.44(6)

C25–H25∙∙∙O17 viii 0.95(1) 2.639(36) 3.336(38) 130.62(5) C26–H26∙∙∙O9 ii 0.95(1) 2.467(36) 2.948(25) 111.30(4)

π···π interactions Cg···Cg (Å)

Cg1∙∙∙Cg2 4.043(24) Symmetry codes: i −x, 1 − y, 1 − z; ii 1 − x, 1 − y, 1 − z; iii 1 − x, 1 − y, −z; iv 1 − x, −y, 1 − z; v −x, −y, 1 − z; vi 1 − x, −y, 2 − z; vii x, y, 1 + z; viii x, 1 + y, z. Cg denotes the centre of gravity of the 6-membered pyridine ring.

Figure 4. The geometry of noncovalent interactions in complex 1: (a) O–H···O, (b) C–H···Ointramolecular, (c) π···π and (d) C–H···O intermolecular (translucent molecules belong to adjacentchains) (Bi—orange, O—red, N—blue, C—black, H—white).


Hydrogen Bonds

Donor–H···Acceptor D–H (Å) H···A (Å) D···A (Å) D–H···A (◦)

O3–H3A···O7 iii 0.84(1) 1.801(28) 2.625(37) 166.46(4)O12–H12A···O1 iv 0.84(1) 2.550(41) 3.171(40) 131.65(5)

O17–H17B···O9 0.87(1) 2.574(14) 3.208(30) 130.56(4)C5–H5···O16 i 0.95(1) 2.220(38) 3.140(51) 162.68(4)

C10–H10···O16 i 0.95(1) 2.489(38) 3.310(47) 144.71(5)C12–H12···O1 0.95(1) 2.542(41) 3.012(42) 110.73(4)

C12–H12···O17 0.95(1) 2.926(38) 3.409(51) 112.79(3)C12–H12···O12 A iv 0.95(1) 2.211(36) 2.957(53) 134.64(4)

C17–H17···O11 vi 0.95(2) 2.519(5) 3.313(13) 141.00(3)C17–H17···O11 A vi 0.95(2) 2.699(41) 3.278(36) 119.81(3)

C18–H18···O2 vii 0.95(2) 2.901(10) 3.496(23) 121.81(3)C19–H19···O7 ii 0.95(1) 2.483(20) 3.346(22) 150.44(6)

C25–H25···O17 viii 0.95(1) 2.639(36) 3.336(38) 130.62(5)C26–H26···O9 ii 0.95(1) 2.467(36) 2.948(25) 111.30(4)

π···π interactions

Cg···Cg (Å)

Cg1···Cg2 4.043(24)

Symmetry codes: i−x, 1 − y, 1 − z; ii 1 − x, 1 − y, 1 − z; iii 1 − x, 1 − y, −z; iv 1 − x, −y, 1 − z; v

−x, −y, 1 − z; vi 1 − x,−y, 2 − z; vii x, y, 1 + z; viii x, 1 + y, z. Cg denotes the centre of gravity of the 6-membered pyridine ring.

Int. J. Mol. Sci. 2020, 21, 8696 9 of 26


In the structure of complex 2, ligand 2,3pydcH exhibited a chelating coordination mode (κ2N,O), while ligand 2,3pydc exhibited a chelating-bridging coordination mode (µ-κ2N,O:κ2O″,O‴) (Figure 5a). Compound 2 was a 1-dimensional coordination polymer forming a zig-zag pattern along the c axis. From the topological point of view, this type of connection is described as 2C1 in the valence-bonded MOFs standard representation. 2-Connected [Bi(2,3pydcH)Cl2] nodes were combined by 2-connected [2,3pydc] linkers at a distance of 8.909 Å. In the H-bonded MOFs standard representation, the topology of complex 2 was changed. Taking into account the strong O4–H4A∙∙∙O6ii hydrogen bonds formed between the –COOH group of the 2,3pydcH ligand and the –COO– group of the 2,3pydc ligand, the dimensionality increased to 2D (bc plane). Nodes and linkers became 3-connected, which resulted in the formation of a honeycomb-like hcb net described by the 63 point symbol (Figure 5b).

Figure 5. (a) Coordination modes of carboxylate ligands in complex 2; (b) a fragment of the 1D crystal structure merged with 2C1 underlying net in valence-bonded MOFs standard representation and a fragment of the 2D crystal structure merged with hcb underlying the net in H-bonded MOFs standard representation for coordination polymer 2 (Bi—orange, O—red, N—blue, Cl—green, C—black, H—white).

The analysis of the complex 2 crystal structure revealed many noncovalent interactions (Figure 6, Table 4). Between the 1D chains, strong O–H(COOH)∙∙∙O(COO) hydrogen bonds (H4A∙∙∙O6ii = 1.727 Å) were formed (Figure 6a). Compound 2 was also stabilized by intra- and interchain C–H∙∙∙∙O hydrogen bonds with d(H∙∙∙O) distances ranging from 2.408 to 2.846 Å. The presence of triethylammonium cations in the structure was the source of many donor C–H and N–H groups, which were the basis of a strong hydrogen-bonded net. The stronger bonds were the N–H(Et3NH)∙∙∙O(COO) bonds formed at d(H∙∙∙N) distances of 1.742 and 1.752 Å (Figure 6b). In turn, coordinated chloride ions served as acceptors in the formation of four-furcated C–H∙∙∙Cl hydrogen bonds with Et3NH cations (Figure 6c). Donor C–H groups of Et3NH molecules also formed interactions with carboxylate oxygen atoms at d(H∙∙∙O) distances of 2.554–2.999 Å (Figure 6d). Weak nonconventional C–H∙∙∙π hydrogen bond type III according to Malone [58] was also found (Figure 6d).

Figure 5. (a) Coordination modes of carboxylate ligands in complex 2; (b) a fragment of the 1Dcrystal structure merged with 2C1 underlying net in valence-bonded MOFs standard representationand a fragment of the 2D crystal structure merged with hcb underlying the net in H-bonded MOFsstandard representation for coordination polymer 2 (Bi—orange, O—red, N—blue, Cl—green, C—black,H—white).

The analysis of the complex 2 crystal structure revealed many noncovalent interactions (Figure 6,Table 4). Between the 1D chains, strong O–H(COOH)···O(COO) hydrogen bonds (H4A···O6ii = 1.727 Å)were formed (Figure 6a). Compound 2 was also stabilized by intra- and interchain C–H····O hydrogenbonds with d(H···O) distances ranging from 2.408 to 2.846 Å. The presence of triethylammoniumcations in the structure was the source of many donor C–H and N–H groups, which were the basis ofa strong hydrogen-bonded net. The stronger bonds were the N–H(Et3NH)···O(COO) bonds formedat d(H···N) distances of 1.742 and 1.752 Å (Figure 6b). In turn, coordinated chloride ions served asacceptors in the formation of four-furcated C–H···Cl hydrogen bonds with Et3NH cations (Figure 6c).Donor C–H groups of Et3NH molecules also formed interactions with carboxylate oxygen atoms atd(H···O) distances of 2.554–2.999 Å (Figure 6d). Weak nonconventional C–H···π hydrogen bond type IIIaccording to Malone [58] was also found (Figure 6d).

2.3. FT-IR Analysis

The FT-IR analysis results of pyridine-2,3-dicarboxylic acid and bismuth(III) complexes 1 and 2are summarized in Table S1. An interesting phenomenon of this acid worth mentioning is that it existsin its zwitterionic form in the solid-state. Therefore, in the free ligand spectrum, we observed a bandderived from protonated pyridine nitrogen (ν(N–H)pyH) and a broad band of O–H stretching vibrationsattributed to intramolecular hydrogen bonds between the carboxylate groups [48,59,60]. The infraredspectra of bismuth coordination polymers 1 and 2 (Figure 7) contained the bands derived from thevibrations ν(C=O)COOH at 1727 and 1708 cm−1, respectively, as well as the vibrations νas(COO) andνs(COO) (Table S1). This spectral pattern indicated that one of the carboxylic groups of the ligand wasdeprotonated while the second one remained deprotonated (mono-deprotonated-2,3pydcH anion),or both carboxylic groups were deprotonated (doubly deprotonated-2,3pydc anion). The ∆ν values ofthe carboxylate stretching frequencies [∆ν = νas(COO) − νs(COO)] [61] were 246, 202 and 165 cm−1

in the spectrum of complex 1 and 249 and 182 cm−1 in the spectrum of complex 2, indicating thedifferent coordination modes of the carboxylates in these compounds. According to Deacon andPhillips [61], the value ∆ν> 200 cm−1 indicated a bridging mode of ligand binding, while ∆ν< 200 cm−1

Int. J. Mol. Sci. 2020, 21, 8696 10 of 26

indicated a bidentate chelating mode. In addition, the FT-IR spectra provided further evidence for theformation of a coordination bond between the Bi(III) ion and the pyridine nitrogen atom by meansof a relative shift in the absorbance of the ν(C=N) band (see Table S1) and a strong absorption bandat 634–624 cm−1 [35,62]. Additionally, in the spectrum of compound 1, a wide band in the range3600–3200 cm−1 from ν(O–H) vibrations corresponding to the water molecules engaged in hydrogenbonds was observed. On the other hand, in the spectrum of compound 2, additional bands appearedat 2712 and 2511 cm−1 and at 1272 cm−1, which were attributed to the ν(N–H) and ν(C–N) vibrations.These bands suggested the presence of protonated triethylammonium (Et3NH) ions in the complexstructure. Thus, spectroscopic analysis showed a good correlation with the structural X-ray analysisresults of the analyzed complexes (vide supra).Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 10 of 26

(a) (c)

(b) (d)

Figure 6. The geometry of noncovalent interactions in complex 2: (a) O/C–H∙∙∙O formed between adjacent polymeric chains, (b) N–H∙∙∙O, (c) C–H∙∙∙Cl and (d) C–H∙∙∙O/π formed between Et3NH cations and polymeric chains (translucent molecules belong to adjacent chains) (Bi—orange, O—red, N—blue, Cl—green, C—black, H—white).


Hydrogen Bonds Donor–H···Acceptor D–H (Å) H···A (Å) D···A (Å) D–H···A (°)

Interchain

O4–H4A∙∙∙O6 ii 0.84 1.727(1) 2.533(1) 160.08 C5–H5∙∙∙O2 iii 0.95 2.846(6) 3.281(6) 109.03 C6–H6∙∙∙O3 iii 0.95 2.654(3) 3.460(3) 143.04 C6–H6∙∙∙O5 0.95 2.408(1) 3.025(1) 122.36

C14–H14∙∙∙O1 iv 0.95 2.585(2) 3.399(2) 143.88 C15–H15∙∙∙O4 v 0.95 2.545(2) 3.323(1) 139.22 C16–H16∙∙∙O6 i 0.95 2.689(1) 3.598(1) 160.22 C16–H16∙∙∙O7 i 0.95 2.661(2) 3.280(2) 123.17

Between Et3NH and polymeric

chain

N2 ii–H2 ii∙∙∙O2 1.00 1.742(1) 2.740(2) 174.95 N3–H3∙∙∙O8 1.00 1.752(2) 2.701(3) 156.94

C26–H26B∙∙∙Cl1 0.97 2.801(4) 3.523(5) 131.09 C27 i–H27B i∙∙∙Cl1 0.99 2.778(3) 3.507(3) 130.83 C29 i–H29B i∙∙∙Cl1 0.98 3.004(5) 3.696(5) 128.49

C30 vi–H30B vi∙∙∙Cl1 0.98 3.058(2) 3.745(2) 128.29 C20 ii–H20A ii∙∙∙Cl2 0.98 1.992(1) 2.458(3) 106.68

Figure 6. The geometry of noncovalent interactions in complex 2: (a) O/C–H···O formed betweenadjacent polymeric chains, (b) N–H···O, (c) C–H···Cl and (d) C–H···O/π formed between Et3NH cationsand polymeric chains (translucent molecules belong to adjacent chains) (Bi—orange, O—red, N—blue,Cl—green, C—black, H—white).

Int. J. Mol. Sci. 2020, 21, 8696 11 of 26


Hydrogen Bonds

Donor–H···Acceptor D–H (Å) H···A (Å) D···A (Å) D–H···A (◦)

Interchain

O4–H4A···O6 ii 0.84 1.727(1) 2.533(1) 160.08C5–H5···O2 iii 0.95 2.846(6) 3.281(6) 109.03C6–H6···O3 iii 0.95 2.654(3) 3.460(3) 143.04C6–H6···O5 0.95 2.408(1) 3.025(1) 122.36

C14–H14···O1 iv 0.95 2.585(2) 3.399(2) 143.88C15–H15···O4 v 0.95 2.545(2) 3.323(1) 139.22C16–H16···O6 i 0.95 2.689(1) 3.598(1) 160.22C16–H16···O7 i 0.95 2.661(2) 3.280(2) 123.17

Between Et3NH andpolymeric chain

N2 ii–H2 ii···O2 1.00 1.742(1) 2.740(2) 174.95

N3–H3···O8 1.00 1.752(2) 2.701(3) 156.94C26–H26B···Cl1 0.97 2.801(4) 3.523(5) 131.09

C27 i–H27B i···Cl1 0.99 2.778(3) 3.507(3) 130.83

C29 i–H29B i···Cl1 0.98 3.004(5) 3.696(5) 128.49

C30 vi–H30B vi···Cl1 0.98 3.058(2) 3.745(2) 128.29

C20 ii–H20A ii···Cl2 0.98 1.992(1) 2.458(3) 106.68

C21–H21A···Cl2 0.99 2.925(1) 3.615(2) 127.11C22–H22A···Cl2 0.99 2.986(2) 3.609(4) 121.93C23–H23A···Cl2 0.99 3.052(1) 4.012(2) 163.96

C19 vii–H19A vii···O7 0.99 2.554(4) 3.410(5) 144.9

C20 ii–H20C ii···O2 0.98 2.986(5) 3.640(5) 125.41

C22 vii–H22B vii···O6 0.98 2.766(3) 3.549(6) 137.45

C23 vii–H23A vii···O7 0.99 2.624(4) 3.475(3) 144.18

C24 ii–H24C ii···O2 0.98 2.840(3) 3.544(6) 129.43

C25–H25B···O6 0.99 2.922(1) 3.396(2) 110.41C26 vi–H26C vi

···O3 0.98 2.642(4) 3.610(6) 170.72C27 vi–H27A vi

···O3 0.99 2.606(3) 3.594(4) 175.75C28–H28B···O8 0.98 2.999(3) 3.600(3) 120.91C30–H30C···O8 0.99 2.919(6) 3.640(8) 130.61

C24–H24C···Cg ii 0.98 2.967(5) 3.627(5) 125.63

Symmetry codes: i x, 0.5 − y, −0.5 + z; ii x, 1.5 − y, −0.5 + z; iii x, 1.5 − y, 0.5 + z; iv x, 0.5 − y, 0.5 + z; v x, −1 + y,z; vi

−x, 0.5 + y, 1.5 − z; vii 1 − x, 1 − y, 2 − z. Cg denotes the centre of gravity of the 6-membered pyridine ring.Et3NH—triethylammonium cation.


Phillips [61], the value Δν > 200 cm−1 indicated a bridging mode of ligand binding, while Δν < 200 cm−1 indicated a bidentate chelating mode. In addition, the FT-IR spectra provided further evidence for the formation of a coordination bond between the Bi(III) ion and the pyridine nitrogen atom by means of a relative shift in the absorbance of the ν(C=N) band (see Table S1) and a strong absorption band at 634–624 cm−1 [35,62]. Additionally, in the spectrum of compound 1, a wide band in the range 3600–3200 cm−1 from ν(O–H) vibrations corresponding to the water molecules engaged in hydrogen bonds was observed. On the other hand, in the spectrum of compound 2, additional bands appeared at 2712 and 2511 cm−1 and at 1272 cm−1, which were attributed to the ν(N–H) and ν(C–N) vibrations. These bands suggested the presence of protonated triethylammonium (Et3NH) ions in the complex structure. Thus, spectroscopic analysis showed a good correlation with the structural X-ray analysis results of the analyzed complexes (vide supra).

(a) (b)

(c) (d)

Figure 7. (a) The non-zwitterionic and zwitterionic form of 2,3pydcH2; the FT-IR spectra of: (b) 2,3pydcH2, (c) complex 1 and (d) complex 2.

2.4. Thermal Analysis

To determine the thermal stability of the Bi(III) complexes, thermogravimetric analysis was carried out. Coordination polymer 1 was stable at temperatures up to 35 °C, and the first decomposition step was attributed to the loss of water molecules (1.59%, calcd: 1.64%) (Figure 8a). Next, at temperatures up to 450 °C, we observed the gradual decomposition of the coordinating mono-deprotonated and deprotonated pyridine-2,3-dicarboxylate anions (55.68%, calcd: 55.92%). At the end of this process, Bi2O3 remained as a final residue (42.73%, calcd: 42.44%). Polymer 2 was stable up to approximately 140 °C and then decomposed in two main stages (Figure 8b). The first stage involved the thermal dissociation of the two lattice triethylammonium cations (25.49%, calcd:

NO

OH

O

OH

N+

O

O

H O

O-H

Figure 7. Cont.

Int. J. Mol. Sci. 2020, 21, 8696 12 of 26


Phillips [61], the value Δν > 200 cm−1 indicated a bridging mode of ligand binding, while Δν < 200 cm−1 indicated a bidentate chelating mode. In addition, the FT-IR spectra provided further evidence for the formation of a coordination bond between the Bi(III) ion and the pyridine nitrogen atom by means of a relative shift in the absorbance of the ν(C=N) band (see Table S1) and a strong absorption band at 634–624 cm−1 [35,62]. Additionally, in the spectrum of compound 1, a wide band in the range 3600–3200 cm−1 from ν(O–H) vibrations corresponding to the water molecules engaged in hydrogen bonds was observed. On the other hand, in the spectrum of compound 2, additional bands appeared at 2712 and 2511 cm−1 and at 1272 cm−1, which were attributed to the ν(N–H) and ν(C–N) vibrations. These bands suggested the presence of protonated triethylammonium (Et3NH) ions in the complex structure. Thus, spectroscopic analysis showed a good correlation with the structural X-ray analysis results of the analyzed complexes (vide supra).

(a) (b)

(c) (d)

Figure 7. (a) The non-zwitterionic and zwitterionic form of 2,3pydcH2; the FT-IR spectra of: (b) 2,3pydcH2, (c) complex 1 and (d) complex 2.


To determine the thermal stability of the Bi(III) complexes, thermogravimetric analysis was carried out. Coordination polymer 1 was stable at temperatures up to 35 °C, and the first decomposition step was attributed to the loss of water molecules (1.59%, calcd: 1.64%) (Figure 8a). Next, at temperatures up to 450 °C, we observed the gradual decomposition of the coordinating mono-deprotonated and deprotonated pyridine-2,3-dicarboxylate anions (55.68%, calcd: 55.92%). At the end of this process, Bi2O3 remained as a final residue (42.73%, calcd: 42.44%). Polymer 2 was stable up to approximately 140 °C and then decomposed in two main stages (Figure 8b). The first stage involved the thermal dissociation of the two lattice triethylammonium cations (25.49%, calcd:

NO

OH

O

OH

N+

O

O

H O

O-H

Figure 7. (a) The non-zwitterionic and zwitterionic form of 2,3pydcH2; the FT-IR spectra of:(b) 2,3pydcH2, (c) complex 1 and (d) complex 2.


To determine the thermal stability of the Bi(III) complexes, thermogravimetric analysis was carriedout. Coordination polymer 1 was stable at temperatures up to 35 ◦C, and the first decomposition stepwas attributed to the loss of water molecules (1.59%, calcd: 1.64%) (Figure 8a). Next, at temperaturesup to 450 ◦C, we observed the gradual decomposition of the coordinating mono-deprotonated anddeprotonated pyridine-2,3-dicarboxylate anions (55.68%, calcd: 55.92%). At the end of this process,Bi2O3 remained as a final residue (42.73%, calcd: 42.44%). Polymer 2 was stable up to approximately140 ◦C and then decomposed in two main stages (Figure 8b). The first stage involved the thermaldissociation of the two lattice triethylammonium cations (25.49%, calcd: 25.06%), which were boundto the coordination polymer chain by hydrogen bonds. In the next stage, which took place in thetemperature range of 210–450 ◦C, the whole polymer was decomposed (observed: 46.29%, calcd:46.37%). The product of the thermal decomposition of 2 was Bi2O3 (28.22%, calcd: 28.57%).Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 13 of 26

(a) (b)

Figure 8. The TG/DTG curves for (a) compound 1 and (b) compound 2.

2.5. Photoluminescence Properties

To establish the photoluminescence properties of the newly obtained Bi(III) coordination polymers 1 and 2, 3D and 2D room temperature solid-state excitation/emission spectra were recorded (Figure 9). Pyridine-2,3-dicarboxylic acid exhibited blue light emission with a maximum at 459 nm after excitation at 419 nm (Figure 9a). The emission of the ligand was attributed to the intraligand (IL) n→π* transitions [63]. The excitation spectrum of 2,3pydcH2 contained an additional band without a distinct maximum below 400 nm, which was attributed to the higher energy π→π* transitions. Comparing the 3D spectrum of compound 1 (Figure 9b) with the 2,3pydcH2 spectrum, the emission centers were located at similar wavelengths. The emission maximum at 452 nm (λex = 413 nm) was only slightly blue-shifted (7 nm) in the spectrum of complex 1 compared to the ligand. The emission band was characterized by a similar ligand Stokes shift (39 nm), which pointed to the intraligand type of electronic transitions in complex 1. The shoulder at ca. 470 nm indicated the presence of two types of ligand in the structure (mono-deprotonated and fully deprotonated), which coordinated to Bi(III) ions in different fashions. Thus, constructed in this way, the polymeric structure is characterized by a different rigidity, which influences the energy of emission. Similarly, compound 2 exhibited blue luminescence with a maximum at 463 and 471 nm after excitation at 362 nm (Figure 9c). Moreover, a significant Stokes shifts (101 and 109 nm) of coordination polymer 2, accompanying by similar excitation wavelength compared to the ligand, suggested that the emission of 2 can be attributed to a ligand-to-metal charge transfer transition (LMCT), as well as to a change in the intraligand transitions (IL) [27,32,64]. The photoluminescence quantum yield of complex 2 was 8.36%, which makes it a good candidate for more specific studies of Bi-based fluorescent materials [62,65].

40

50

60

70

80

90

100 (1)

Temperature (°C)

TG

DTG

Mas

s (%

)

100 200 300 400 500 600 700

10

20

30

40

50

60

70

80

90

100 (2)

Temperature (°C)

TG

DTG

Mas

s (%

)

100 200 300 400 500 600 700

Figure 8. The TG/DTG curves for (a) compound 1 and (b) compound 2.

2.5. Photoluminescence Properties

To establish the photoluminescence properties of the newly obtained Bi(III) coordination polymers1 and 2, 3D and 2D room temperature solid-state excitation/emission spectra were recorded (Figure 9).Pyridine-2,3-dicarboxylic acid exhibited blue light emission with a maximum at 459 nm after excitationat 419 nm (Figure 9a). The emission of the ligand was attributed to the intraligand (IL) n→π*transitions [63]. The excitation spectrum of 2,3pydcH2 contained an additional band without a distinct

Int. J. Mol. Sci. 2020, 21, 8696 13 of 26

maximum below 400 nm, which was attributed to the higher energy π→π* transitions. Comparingthe 3D spectrum of compound 1 (Figure 9b) with the 2,3pydcH2 spectrum, the emission centerswere located at similar wavelengths. The emission maximum at 452 nm (λex = 413 nm) was onlyslightly blue-shifted (7 nm) in the spectrum of complex 1 compared to the ligand. The emission bandwas characterized by a similar ligand Stokes shift (39 nm), which pointed to the intraligand type ofelectronic transitions in complex 1. The shoulder at ca. 470 nm indicated the presence of two typesof ligand in the structure (mono-deprotonated and fully deprotonated), which coordinated to Bi(III)ions in different fashions. Thus, constructed in this way, the polymeric structure is characterized bya different rigidity, which influences the energy of emission. Similarly, compound 2 exhibited blueluminescence with a maximum at 463 and 471 nm after excitation at 362 nm (Figure 9c). Moreover,a significant Stokes shifts (101 and 109 nm) of coordination polymer 2, accompanying by similarexcitation wavelength compared to the ligand, suggested that the emission of 2 can be attributed to aligand-to-metal charge transfer transition (LMCT), as well as to a change in the intraligand transitions(IL) [27,32,64]. The photoluminescence quantum yield of complex 2 was 8.36%, which makes it a goodcandidate for more specific studies of Bi-based fluorescent materials [62,65].Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 14 of 26

(a) (b) (c)

Figure 9. The solid-state 3D (top) and 2D (bottom) photoluminescence spectra of: (a) 2,3pydcH2, (b) compound 1 and (c) compound 2.

2.6. Solubility and Stability

Solubility and stability studies are important in the process of developing biologically active compounds. The ligand 2,3pydcH2 is soluble in H2O, 1 M HCl, MeOH, EtOH, DMF and DMSO, partly soluble in iPrOH and MeCN, and insoluble in Me2CO, THF and CH2Cl2. However, coordination polymers 1 and 2 were soluble only in DMSO and 1 M HCl but insoluble in the other tested solvents. An important advantage of the tested bismuth compounds was their solubility in DMSO without subsequent precipitation after diluting it with water. It is an essential feature of compounds in further biological studies conducted against Helicobacter pylori.

It is also important to examine the stability of analyzed compounds in the media used in the anti-H. pylori experiments. All tested compounds (2,3pydcH2, complexes 1 and 2) were stable for 48 h when dissolved in DMSO and then diluted with H2O (1:50 v/v). According to the time-dependent UV-Vis spectra (Figure 10 (top)), there were no obvious changes in the positions of the absorption bands (±1 nm) and no significant decrease in absorbance. The absorption maxima were located at 236 and 274 nm for complex 1 and at 237 and 275 nm for complex 2 (Figure 10b,c (top)); the maxima were located almost at the same positions as the maxima in the ligand spectrum (234 and 275 nm) (Figure 10a (top)). Comparing the free ligand spectrum with the electronic spectra of complexes 1 and 2 showed the main bands corresponding to the ligand centered in the π→π* and n→π* transitions. Therefore, it can be assumed that there were no structural changes of the compounds upon their reaction with solvent (DMSO and H2O) molecules.

350 400 450 500 550 600

459 nm419 nm 2,3pydcH2 emission excitation

Inte

nsity

(a.u

.)

Wavelength (nm)250 300 350 400 450 500 550 600 650

470 nm

413 nm399 nm

452 nm

(1) emission excitation

Inte

nsity

(a.u

.)

Wavelength (nm)250 300 350 400 450 500 550 600 650

471 nm463 nm362 nm (2) emission excitation

Inte

nsity

(a.u

.)

Wavelength (nm)

Figure 9. The solid-state 3D (top) and 2D (bottom) photoluminescence spectra of: (a) 2,3pydcH2, (b)compound 1 and (c) compound 2.

2.6. Solubility and Stability

Solubility and stability studies are important in the process of developing biologically activecompounds. The ligand 2,3pydcH2 is soluble in H2O, 1 M HCl, MeOH, EtOH, DMF and DMSO,partly soluble in iPrOH and MeCN, and insoluble in Me2CO, THF and CH2Cl2. However, coordinationpolymers 1 and 2 were soluble only in DMSO and 1 M HCl but insoluble in the other tested solvents.An important advantage of the tested bismuth compounds was their solubility in DMSO withoutsubsequent precipitation after diluting it with water. It is an essential feature of compounds in furtherbiological studies conducted against Helicobacter pylori.

It is also important to examine the stability of analyzed compounds in the media used in theanti-H. pylori experiments. All tested compounds (2,3pydcH2, complexes 1 and 2) were stable for 48 hwhen dissolved in DMSO and then diluted with H2O (1:50 v/v). According to the time-dependent

Int. J. Mol. Sci. 2020, 21, 8696 14 of 26

UV-Vis spectra (Figure 10 (top)), there were no obvious changes in the positions of the absorptionbands (±1 nm) and no significant decrease in absorbance. The absorption maxima were located at236 and 274 nm for complex 1 and at 237 and 275 nm for complex 2 (Figure 10b,c (top)); the maximawere located almost at the same positions as the maxima in the ligand spectrum (234 and 275 nm)(Figure 10a (top)). Comparing the free ligand spectrum with the electronic spectra of complexes 1 and2 showed the main bands corresponding to the ligand centered in the π→π* and n→π* transitions.Therefore, it can be assumed that there were no structural changes of the compounds upon theirreaction with solvent (DMSO and H2O) molecules.Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 16 of 27

(a) (b) (c)

Figure 10. Time-dependent (0 h, 24 h and 48 h) stability studies on: (a) 2,3pydcH2, (b) complex 1, (c) complex 2 in DMSO/H2O 1:50 (v/v) (top) and DMSO/1M HCl 1:50 (v/v) (bottom) solutions monitored by UV-Vis absorption spectra.

Additionally, it is important to examine the behavior of complexes 1 and 2 in acidic medium, taking into consideration that the compounds would be exposed to stomach acid in vivo if used as drugs [66]. After dissolving the compounds in 1 M HCl solution, the UV-vis spectra showed an additional absorption band near 321 nm, which confirmed that the complexes released organic acids and Bi3+ ions, which remained soluble in HCl solution as BiOCl [67]. A similar UV-Vis spectrum was recorded for the model reaction of BiCl3 with H2O in a 1 M HCl solution (Figure S1).

2.7. Antibacterial Activity towards Helicobacter Pylori

Infection with H. pylori bacteria contributes to the development of three serious digestive diseases, namely, gastric and duodenal ulcers, gastric cancer and MALT-type gastric lymphoma. The discovery of this relationship has led to extensive research regarding the application of bismuth compounds in the treatment of microbial infections [21,40]. The most important research studies include Bi(III) complexes with non-steroidal anti-inflammatory drugs [68], indolocarboxylates [67], salicylates [69–71], sulfonates [72–74], (thio)saccharinates [75], acetosulfame and cyclamic acid [76] and (benzo)hydroxamic acids [77,78]. Most of the compounds from these groups are heteroleptic organometallic complexes, including oxoclasters. A great advantage of the use of bismuth-based drugs is the lack of H. pylori resistance towards these drugs [22,41,79–81]. These studies inspired us to examine the antimicrobial properties of new polymeric Bi(III) complexes with low-molecular weight N-heteroaromatic carboxylic acids against Helicobacter pylori.

An analysis of the obtained results (Figure 11) revealed that the ligand 2,3pydcH2 was inactive against both H. pylori strains (26695 and N6), even at high concentrations (MIC > 100 μM). Both Bi(III) complexes exhibited bacteriostatic effects towards H. pylori. The MIC values of 1 and 2 towards reference strain 26695 reached values of 13.7 and 36.8 μM, respectively. The results indicated that the compound 1 was about twice as potent against H. pylori than the commercially used Bi-based drug BSS (MIC = 34.5 μM). Moreover, strain N6 was slightly more sensitive to compound 1 (MIC = 11.4 μM) and compound 2 (MIC = 24.5 μM) than strain 26695. Generally, compound 1 was more than twice as active against H. pylori as compound 2. It can be concluded that the presence of chloride and triethylammonium ions in the structure of complex 2 pointed out the anionic form of Bi(III) complex, which influenced its antibacterial activity. The anionic form of complex 2 is more difficult to penetrate the negatively charged cell membrane of the H. pylori bacteria.

Figure 10. Time-dependent (0 h, 24 h and 48 h) stability studies on: (a) 2,3pydcH2, (b) complex 1,(c) complex 2 in DMSO/H2O 1:50 (v/v) (top) and DMSO/1M HCl 1:50 (v/v) (bottom) solutions monitoredby UV-Vis absorption spectra.

Additionally, it is important to examine the behavior of complexes 1 and 2 in acidic medium,taking into consideration that the compounds would be exposed to stomach acid in vivo if used asdrugs [66]. After dissolving the compounds in 1 M HCl solution, the UV-vis spectra showed anadditional absorption band near 321 nm, which confirmed that the complexes released organic acidsand Bi3+ ions, which remained soluble in HCl solution as BiOCl [67]. A similar UV-Vis spectrum wasrecorded for the model reaction of BiCl3 with H2O in a 1 M HCl solution (Figure S1).

2.7. Antibacterial Activity towards Helicobacter Pylori

Infection with H. pylori bacteria contributes to the development of three serious digestive diseases,namely, gastric and duodenal ulcers, gastric cancer and MALT-type gastric lymphoma. The discoveryof this relationship has led to extensive research regarding the application of bismuth compoundsin the treatment of microbial infections [21,40]. The most important research studies include Bi(III)complexes with non-steroidal anti-inflammatory drugs [68], indolocarboxylates [67], salicylates [69–71],sulfonates [72–74], (thio)saccharinates [75], acetosulfame and cyclamic acid [76] and (benzo)hydroxamicacids [77,78]. Most of the compounds from these groups are heteroleptic organometallic complexes,including oxoclasters. A great advantage of the use of bismuth-based drugs is the lack of H. pyloriresistance towards these drugs [22,41,79–81]. These studies inspired us to examine the antimicrobialproperties of new polymeric Bi(III) complexes with low-molecular weight N-heteroaromatic carboxylicacids against Helicobacter pylori.

Int. J. Mol. Sci. 2020, 21, 8696 15 of 26

An analysis of the obtained results (Figure 11) revealed that the ligand 2,3pydcH2 was inactiveagainst both H. pylori strains (26695 and N6), even at high concentrations (MIC > 100 µM). Both Bi(III)complexes exhibited bacteriostatic effects towards H. pylori. The MIC values of 1 and 2 towardsreference strain 26695 reached values of 13.7 and 36.8 µM, respectively. The results indicated that thecompound 1 was about twice as potent against H. pylori than the commercially used Bi-based drug BSS(MIC = 34.5 µM). Moreover, strain N6 was slightly more sensitive to compound 1 (MIC = 11.4 µM)and compound 2 (MIC = 24.5 µM) than strain 26695. Generally, compound 1 was more than twiceas active against H. pylori as compound 2. It can be concluded that the presence of chloride andtriethylammonium ions in the structure of complex 2 pointed out the anionic form of Bi(III) complex,which influenced its antibacterial activity. The anionic form of complex 2 is more difficult to penetratethe negatively charged cell membrane of the H. pylori bacteria.Int. J. Mol. Sci. 2020, 21, x FOR PEER REVIEW 16 of 26

Figure 11. Antibacterial activity of [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1), {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2), pyridine-2,3-dicarboxylic acid (2,3pydcH2) and bismuth subsalicylate (BSS) against H. pylori strains 26695 and N6.

Comparing the antimicrobial activity of 1 and 2 with literature data for Bi(III)-carboxylate complexes, it was concluded that the obtained compounds exhibited a slightly smaller bacteriostatic effect towards H. pylori (Table 5). The reason for the lower activity could be explained by taking into consideration the polymeric form of the complexes and the different coordination environments, including not only oxygen but also nitrogen/chloride donor atoms and much more complicated forms of coordination polyhedra.

Table 5. Antibacterial activity of Bi(III) carboxylate complexes against Helicobacter pylori strain 26695.

Compound Representation of Bi(III) Coordination Chromophore MIC µg mL−1

(µM) Ref.

Pyridinedicarboxylic acid

[Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1)

{BiO7N2} 15.0 (13.7)

This work

{(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n

(2)

{BiO4N2Cl2} 30.0 (36.8)

BSS 12.5 (34.5) Indolecarboxylic acid

[Bi(IAA)3]

[Bi(IAA)3]

{BiO6} 6.25 (8.54)

[67]

[Bi(IPA)3] {BiO6} 6.25 (8.07) [Bi(IBA)3] {BiO6} 6.25 (7.66)

[Bi(MICA)3] {BiO6} 6.25 (8.54)

[Bi(IGA)3] {BiO6} 6.25 (8.08)

BSS 12.5 (34.5) Acetylsalicylic acid

Figure 11. Antibacterial activity of [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1), {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2), pyridine-2,3-dicarboxylic acid (2,3pydcH2) and bismuth subsalicylate (BSS)against H. pylori strains 26695 and N6.

Comparing the antimicrobial activity of 1 and 2 with literature data for Bi(III)-carboxylatecomplexes, it was concluded that the obtained compounds exhibited a slightly smaller bacteriostaticeffect towards H. pylori (Table 5). The reason for the lower activity could be explained by takinginto consideration the polymeric form of the complexes and the different coordination environments,including not only oxygen but also nitrogen/chloride donor atoms and much more complicated formsof coordination polyhedra.

Int. J. Mol. Sci. 2020, 21, 8696 16 of 26


Compound Representation of Bi(III)Coordination Chromophore MIC µg mL−1

(µM) Ref.


[Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1)






(µM) Ref.


[Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1)

{BiO7N2} 15.0 (13.7)

This work


(2)

{BiO4N2Cl2} 30.0 (36.8)


[Bi(IAA)3]

[Bi(IAA)3]

{BiO6} 6.25 (8.54)

[67]


[Bi(MICA)3] {BiO6} 6.25 (8.54)

[Bi(IGA)3] {BiO6} 6.25 (8.08)


{BiO7N2} 15.0 (13.7)

This work

{(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2)






(µM) Ref.


[Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1)

{BiO7N2} 15.0 (13.7)

This work


(2)

{BiO4N2Cl2} 30.0 (36.8)


[Bi(IAA)3]

[Bi(IAA)3]

{BiO6} 6.25 (8.54)

[67]


[Bi(MICA)3] {BiO6} 6.25 (8.54)

[Bi(IGA)3] {BiO6} 6.25 (8.08)


{BiO4N2Cl2} 30.0 (36.8)

BSS 12.5 (34.5)

Indolecarboxylic acid

[Bi(IAA)3]






(µM) Ref.


[Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1)

{BiO7N2} 15.0 (13.7)

This work


(2)

{BiO4N2Cl2} 30.0 (36.8)


[Bi(IAA)3]

[Bi(IAA)3]

{BiO6} 6.25 (8.54)

[67]


[Bi(MICA)3] {BiO6} 6.25 (8.54)

[Bi(IGA)3] {BiO6} 6.25 (8.08)


[Bi(IAA)3]

{BiO6} 6.25 (8.54)

[67]

[Bi(IPA)3] {BiO6} 6.25 (8.07)

[Bi(IBA)3] {BiO6} 6.25 (7.66)

[Bi(MICA)3] {BiO6} 6.25 (8.54)

[Bi(IGA)3] {BiO6} 6.25 (8.08)

BSS 12.5 (34.5)

Acetylsalicylic acid

[Bi(asp)3]∞


[Bi(asp)3]∞

[Bi(asp)3]∞

{BiO8} 6.25 (8.37)

[70] [KBi(asp)4]∞ {BiO9} 6.25 (6.48)

NSAIDs

[Bi(L1)3∙H2O]

[Bi(Ketoprofen)3∙H2O]

{BiO6} ≥6.25 (6.35)

[68]

≥6.25 (4.85)

[Bi(L2)3] {BiO6}

≥6.25 (7.01) ≥6.25 (7.58) ≥6.25 (6.47) ≥6.25 (8.67) ≥6.25 (6.75) ≥6.25 (6.55) ≥6.25 (6.33) ≥6.25 (5.97)

BSS ≥12.5 (34.5) 2,3pydcH2—pyridine-2,3-dicarboxylic acid; Et3N—triethylamine; BSS—bismuth subsalicylate; IAA-H—2-(1H-indol-3-yl)acetic acid, IPA-H—3-(1H-indol-3-yl)propanoic acid, IBA-H—4-(1H-indol-3-yl))butanoic acid, IGA-H—2-(1H-indol-3-yl))-2-oxoacetic acid, MICA-H—1-methyl-1H-indole-3-carboxylic acid; aspH—acetylsalicylic acid; NSAIDs: L1: Ketoprofen, Sulindac; L2: Naproxen, Ibuprofen, Fenbufen, 5-Chlorosalicylic acid, Mefenamic acid, Diflunisal, Tolfenamic acid, Flufenamic acid.

3. Experimental

3.1. Materials and Physicochemical Measurements

Chemical reagents were purchased commercially and used as received without further purification; Bi(NO3)3∙5H2O (POCH S.A., Gliwice, Poland), BiCl3 (Sigma-Aldrich, Steinheim, Germany), pyridine-2,3-dicarboxylic acid (Sigma-Aldrich, Steinheim, Germany), triethylamine (POCH S.A., Gliwice, Poland) and all organic solvents (Chempur, Piekary Śląskie, Poland). Elemental analysis (CHNS) was performed on an Elementar Vario Micro Cube analyzer (Elementar, Langenselbold, Germany). FT-IR spectra were recorded on a Nicolet 380 FT-IR type spectrophotometer (Thermo Scientific, Waltham, MA, USA), in the spectral range 4000–500 cm−1, using the ATR-diffusive reflection method. The thermal analysis (TG/DTG) was carried out using a TG/SDTA 851e Mettler-Toledo thermobalance (Columbus, OH, USA). The experiments were performed in air atmosphere, at a heating rate of 5 °C min−1, in the temperature range of 25–700 °C, using α-Al2O3 crucible.

3.2. Synthesis of [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1)

An aqueous solution (30 mL) of pyridine-2,3-dicarboxylic acid (0.75 mmol, 0.1253 g) was heated to about 100 °C. Next solid bismuth(III) nitrate (0.25 mmol, 0.1213 g) was added to the boiling solution. The resulting mixture was stirred and heated under a reflux for 8 h, after which it was filtered off. The clear filtrate was left to crystallize slowly at room temperature. After a week, colourless crystals were formed, collected by filtration and dried under vacuum (m = 0.0321 g (0.0292 mmol), yield: 23%, based on Bi(III) salt) (Scheme 2). Elemental analysis calculated for C28H16N4O17Bi2 (Mr = 1098.41) (%): C 30.62, H 1.47, N 5.10; found: C 30.43, H 1.40, N 5.17; FT-IR (cm−1): 3600–3200 (vb), 2887 (w), 1727 (m), 1657 (m), 1618 (m), 1604 (m), 1574 (s), 1537 (m), 1449 (w), 1372 (s), 1280 (m), 1254 (w), 1230 (m), 1149 (w), 1099 (s), 1071 (w), 1003 (w), 875 (w), 834 (m), 819 (m), 798 (w), 778 (w), 697 (s), 667 (m), 604 (m), 560 (m), 522 (m), 507 (w).

3.3. Synthesis of {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2)

[Bi(asp)3]∞

{BiO8} 6.25 (8.37)

[70][KBi(asp)4]∞ {BiO9} 6.25 (6.48)

NSAIDs

[Bi(L1)3·H2O]


[Bi(asp)3]∞

[Bi(asp)3]∞

{BiO8} 6.25 (8.37)

[70] [KBi(asp)4]∞ {BiO9} 6.25 (6.48)

NSAIDs

[Bi(L1)3∙H2O]

[Bi(Ketoprofen)3∙H2O]

{BiO6} ≥6.25 (6.35)

[68]

≥6.25 (4.85)

[Bi(L2)3] {BiO6}

≥6.25 (7.01) ≥6.25 (7.58) ≥6.25 (6.47) ≥6.25 (8.67) ≥6.25 (6.75) ≥6.25 (6.55) ≥6.25 (6.33) ≥6.25 (5.97)

BSS ≥12.5 (34.5) 2,3pydcH2—pyridine-2,3-dicarboxylic acid; Et3N—triethylamine; BSS—bismuth subsalicylate; IAA-H—2-(1H-indol-3-yl)acetic acid, IPA-H—3-(1H-indol-3-yl)propanoic acid, IBA-H—4-(1H-indol-3-yl))butanoic acid, IGA-H—2-(1H-indol-3-yl))-2-oxoacetic acid, MICA-H—1-methyl-1H-indole-3-carboxylic acid; aspH—acetylsalicylic acid; NSAIDs: L1: Ketoprofen, Sulindac; L2: Naproxen, Ibuprofen, Fenbufen, 5-Chlorosalicylic acid, Mefenamic acid, Diflunisal, Tolfenamic acid, Flufenamic acid.

3. Experimental


Chemical reagents were purchased commercially and used as received without further purification; Bi(NO3)3∙5H2O (POCH S.A., Gliwice, Poland), BiCl3 (Sigma-Aldrich, Steinheim, Germany), pyridine-2,3-dicarboxylic acid (Sigma-Aldrich, Steinheim, Germany), triethylamine (POCH S.A., Gliwice, Poland) and all organic solvents (Chempur, Piekary Śląskie, Poland). Elemental analysis (CHNS) was performed on an Elementar Vario Micro Cube analyzer (Elementar, Langenselbold, Germany). FT-IR spectra were recorded on a Nicolet 380 FT-IR type spectrophotometer (Thermo Scientific, Waltham, MA, USA), in the spectral range 4000–500 cm−1, using the ATR-diffusive reflection method. The thermal analysis (TG/DTG) was carried out using a TG/SDTA 851e Mettler-Toledo thermobalance (Columbus, OH, USA). The experiments were performed in air atmosphere, at a heating rate of 5 °C min−1, in the temperature range of 25–700 °C, using α-Al2O3 crucible.


An aqueous solution (30 mL) of pyridine-2,3-dicarboxylic acid (0.75 mmol, 0.1253 g) was heated to about 100 °C. Next solid bismuth(III) nitrate (0.25 mmol, 0.1213 g) was added to the boiling solution. The resulting mixture was stirred and heated under a reflux for 8 h, after which it was filtered off. The clear filtrate was left to crystallize slowly at room temperature. After a week, colourless crystals were formed, collected by filtration and dried under vacuum (m = 0.0321 g (0.0292 mmol), yield: 23%, based on Bi(III) salt) (Scheme 2). Elemental analysis calculated for C28H16N4O17Bi2 (Mr = 1098.41) (%): C 30.62, H 1.47, N 5.10; found: C 30.43, H 1.40, N 5.17; FT-IR (cm−1): 3600–3200 (vb), 2887 (w), 1727 (m), 1657 (m), 1618 (m), 1604 (m), 1574 (s), 1537 (m), 1449 (w), 1372 (s), 1280 (m), 1254 (w), 1230 (m), 1149 (w), 1099 (s), 1071 (w), 1003 (w), 875 (w), 834 (m), 819 (m), 798 (w), 778 (w), 697 (s), 667 (m), 604 (m), 560 (m), 522 (m), 507 (w).


[Bi(Ketoprofen)3·H2O]

{BiO6} ≥6.25 (6.35)

[68]

≥6.25 (4.85)

[Bi(L2)3] {BiO6}

≥6.25 (7.01)

≥6.25 (7.58)≥6.25 (6.47)≥6.25 (8.67)≥6.25 (6.75)≥6.25 (6.55)≥6.25 (6.33)≥6.25 (5.97)

BSS ≥12.5 (34.5)

2,3pydcH2—pyridine-2,3-dicarboxylic acid; Et3N—triethylamine; BSS—bismuth subsalicylate; IAA-H—2-(1H-indol-3-yl)acetic acid, IPA-H—3-(1H-indol-3-yl)propanoic acid, IBA-H—4-(1H-indol-3-yl))butanoic acid,IGA-H—2-(1H-indol- 3-yl))-2-oxoacetic acid, MICA-H—1-methyl-1H-indole-3-carboxylic acid; aspH—acetylsalicylicacid; NSAIDs: L1: Ketoprofen, Sulindac; L2: Naproxen, Ibuprofen, Fenbufen, 5-Chlorosalicylic acid, Mefenamicacid, Diflunisal, Tolfenamic acid, Flufenamic acid.

3. Experimental


Chemical reagents were purchased commercially and used as received without furtherpurification; Bi(NO3)3·5H2O (POCH S.A., Gliwice, Poland), BiCl3 (Sigma-Aldrich, Steinheim,

Int. J. Mol. Sci. 2020, 21, 8696 17 of 26

Germany), pyridine-2,3-dicarboxylic acid (Sigma-Aldrich, Steinheim, Germany), triethylamine(POCH S.A., Gliwice, Poland) and all organic solvents (Chempur, Piekary Slaskie, Poland).Elemental analysis (CHNS) was performed on an Elementar Vario Micro Cube analyzer (Elementar,Langenselbold, Germany). FT-IR spectra were recorded on a Nicolet 380 FT-IR type spectrophotometer(Thermo Scientific, Waltham, MA, USA), in the spectral range 4000–500 cm−1, using the ATR-diffusivereflection method. The thermal analysis (TG/DTG) was carried out using a TG/SDTA 851e Mettler-Toledothermobalance (Columbus, OH, USA). The experiments were performed in air atmosphere, at a heatingrate of 5 ◦C min−1, in the temperature range of 25–700 ◦C, using α-Al2O3 crucible.


An aqueous solution (30 mL) of pyridine-2,3-dicarboxylic acid (0.75 mmol, 0.1253 g) was heatedto about 100 ◦C. Next solid bismuth(III) nitrate (0.25 mmol, 0.1213 g) was added to the boiling solution.The resulting mixture was stirred and heated under a reflux for 8 h, after which it was filtered off.The clear filtrate was left to crystallize slowly at room temperature. After a week, colourless crystalswere formed, collected by filtration and dried under vacuum (m = 0.0321 g (0.0292 mmol), yield: 23%,based on Bi(III) salt) (Scheme 2). Elemental analysis calculated for C28H16N4O17Bi2 (Mr = 1098.41) (%):C 30.62, H 1.47, N 5.10; found: C 30.43, H 1.40, N 5.17; FT-IR (cm−1): 3600–3200 (vb), 2887 (w), 1727(m), 1657 (m), 1618 (m), 1604 (m), 1574 (s), 1537 (m), 1449 (w), 1372 (s), 1280 (m), 1254 (w), 1230 (m),1149 (w), 1099 (s), 1071 (w), 1003 (w), 875 (w), 834 (m), 819 (m), 798 (w), 778 (w), 697 (s), 667 (m), 604(m), 560 (m), 522 (m), 507 (w).


An acetonitrile solution (10 mL) of triethylamine (0.75 mmol, 0.0759 g) was added to 40 mL of acetonitrile solution of pyridine-2,3-dicarboxylic acid (0.75 mmol, 0.1253 g). To the boiling solution was added solid bismuth(III) chloride (0.25 mmol, 0.0788 g). The obtained mixture was heated for next 6 h under a reflux. The resulting mixture was filtered off and left at room temperature to evaporate slowly. After a week, colourless crystals were collected by filtration and dried under vacuum (m = 0.04479 g (0.0549 mmol), yield: 22%, based on Bi(III) salt) (Scheme 2). Elemental analysis calculated for C26H39N4O8Cl2Bi (Mr = 815.49) (%): C 38.29, H 4.82, N 6.87; found: C 38.14, H 4.65, N 6.78; FT-IR (cm−1): 2984 (w), 2712 (w), 2511 (b), 17708 (m), 1651 (w), 1618 (s), 1573 (s), 1563 (s), 1479 (w), 1445 (w), 1441 (m), 1395 (m), 1381 (m), 1370 (s), 1350 (w), 1272 (s), 1221 (w), 1140 (m), 1094 (m), 1063 (w), 1015 (w), 873 (m), 834 (m), 800 (m), 782 (w), 749 (m), 694 (w), 660 (m), 611 (w), 557 (w), 540 (w), 517 (w).

Scheme 2. General reaction conditions employed in the synthesis of Bi(III) coordination polymers (1 and 2).

3.4. Crystal Data Collection and Refinement

Diffraction data were collected on an IPDS 2T dual-beam diffractometer (STOE & Cie GmbH, Darmstadt, Germany) at 120.0(2) K with Mo Kα radiation of the microfocus X-ray source (GeniX 3D Mo High Flux, Xenocs, 50 kV, 1.0 mA, λ= 0.71069 Å). The crystal was thermostated in a nitrogen stream at 120 K using the CryoStream-800 device (Oxford CryoSystem, Long Hanborough, UK) during the entire experiment. Data collection and data reduction were controlled by the X-Area 1.75 program (STOE) [82]. Owing to the high absorption coefficients (11.345 and 5.742 mm−1), numerical absorption corrections were applied based on measured crystal faces. The structures of 1 and 2 were solved with the ShelXT [83] structure solution programs run under Olex2 [84] using Intrinsic Phasing and refined with the ShelXL [85] refinement package. The WinGX [86] program was used to prepare the final version of CIF files. Diamond [87] was used to prepare the figures. All C–H type hydrogen atoms were attached at their geometrically expected positions and refined as riding on heavier atoms with the usual constraints. Positions of the N–H and O–H hydrogen atoms were calculated geometrically and taken into account with isotropic temperature factors and refined as constrained, using the AFIX 13 (for N–H), AFIX 6 and AFIX 147 (for O–H) instructions. Aromatic ring (N3, C15–C19) together with the carboxylate group C(21)O(11)O(12)H(12a) in 1 was found disordered in two positions with probabilities of 0.60(2) and 0.40(2). One atom Cl2 and five ethyl groups in 2 have been modelled as disordered: Cl2 (s.o.f. 0.69(13)/0.31(13)); C19–C20 (s.o.f. 0.71(4)/0.29(4)); C21–C22 (s.o.f. 0.52(8)/0.48(8)); C23–C24 (s.o.f. 0.86(3)/0.14(3)); C25–C26 (s.o.f. 0.51(4)/0.49(4)); C29–C30 (s.o.f. 0.63(5)/0.37(5)). In compounds 1 and 2, residual electron density is somewhat high and localizes near the heavier Bi atom. In our opinion it is an artefact (e.g., due to cut of Fourier series), since no atom can be present at that location. A summary of crystallographic data is shown in Table 6. Crystallographic data for structure of 1 and 2 reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications No. CCDC 1911680 and 1911679. Copies of the data can be obtained free of charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: (+44)-1223-336-033; E-mail: [email protected]).

Scheme 2. General reaction conditions employed in the synthesis of Bi(III) coordination polymers(1 and 2).


An acetonitrile solution (10 mL) of triethylamine (0.75 mmol, 0.0759 g) was added to 40 mL ofacetonitrile solution of pyridine-2,3-dicarboxylic acid (0.75 mmol, 0.1253 g). To the boiling solutionwas added solid bismuth(III) chloride (0.25 mmol, 0.0788 g). The obtained mixture was heatedfor next 6 h under a reflux. The resulting mixture was filtered off and left at room temperatureto evaporate slowly. After a week, colourless crystals were collected by filtration and dried undervacuum (m = 0.04479 g (0.0549 mmol), yield: 22%, based on Bi(III) salt) (Scheme 2). Elemental analysiscalculated for C26H39N4O8Cl2Bi (Mr = 815.49) (%): C 38.29, H 4.82, N 6.87; found: C 38.14, H 4.65,N 6.78; FT-IR (cm−1): 2984 (w), 2712 (w), 2511 (b), 17708 (m), 1651 (w), 1618 (s), 1573 (s), 1563 (s),1479 (w), 1445 (w), 1441 (m), 1395 (m), 1381 (m), 1370 (s), 1350 (w), 1272 (s), 1221 (w), 1140 (m), 1094 (m),1063 (w), 1015 (w), 873 (m), 834 (m), 800 (m), 782 (w), 749 (m), 694 (w), 660 (m), 611 (w), 557 (w), 540 (w),517 (w).

3.4. Crystal Data Collection and Refinement

Diffraction data were collected on an IPDS 2T dual-beam diffractometer (STOE & Cie GmbH,Darmstadt, Germany) at 120.0(2) K with Mo Kα radiation of the microfocus X-ray source (GeniX 3DMo High Flux, Xenocs, 50 kV, 1.0 mA, λ= 0.71069 Å). The crystal was thermostated in a nitrogen streamat 120 K using the CryoStream-800 device (Oxford CryoSystem, Long Hanborough, UK) during the

Int. J. Mol. Sci. 2020, 21, 8696 18 of 26

entire experiment. Data collection and data reduction were controlled by the X-Area 1.75 program(STOE) [82]. Owing to the high absorption coefficients (11.345 and 5.742 mm−1), numerical absorptioncorrections were applied based on measured crystal faces. The structures of 1 and 2 were solved withthe ShelXT [83] structure solution programs run under Olex2 [84] using Intrinsic Phasing and refinedwith the ShelXL [85] refinement package. The WinGX [86] program was used to prepare the finalversion of CIF files. Diamond [87] was used to prepare the figures. All C–H type hydrogen atoms wereattached at their geometrically expected positions and refined as riding on heavier atoms with theusual constraints. Positions of the N–H and O–H hydrogen atoms were calculated geometrically andtaken into account with isotropic temperature factors and refined as constrained, using the AFIX 13(for N–H), AFIX 6 and AFIX 147 (for O–H) instructions. Aromatic ring (N3, C15–C19) together with thecarboxylate group C(21)O(11)O(12)H(12a) in 1 was found disordered in two positions with probabilitiesof 0.60(2) and 0.40(2). One atom Cl2 and five ethyl groups in 2 have been modelled as disordered:Cl2 (s.o.f. 0.69(13)/0.31(13)); C19–C20 (s.o.f. 0.71(4)/0.29(4)); C21–C22 (s.o.f. 0.52(8)/0.48(8)); C23–C24(s.o.f. 0.86(3)/0.14(3)); C25–C26 (s.o.f. 0.51(4)/0.49(4)); C29–C30 (s.o.f. 0.63(5)/0.37(5)). In compounds1 and 2, residual electron density is somewhat high and localizes near the heavier Bi atom. In ouropinion it is an artefact (e.g., due to cut of Fourier series), since no atom can be present at that location.A summary of crystallographic data is shown in Table 6. Crystallographic data for structure of 1 and2 reported in this paper have been deposited with the Cambridge Crystallographic Data Centre assupplementary publications No. CCDC 1911680 and 1911679. Copies of the data can be obtained freeof charge on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: (+44)-1223-336-033;E-mail: [email protected]).

Table 6. Crystal data and structure refinement for 1 and 2.

Empirical Formula C28H16Bi2N4O17 C26H39BiCl2N4O8

CCDC number 1911680 1911679

Formula weight (g mol−1) 1098.41 815.49Temperature (K) 120(2) 120(2)Wavelength (Å) 0.71073 0.71073

Crystal system, space group Triclinic, P-1 Monoclinic, P21/c

Unit cell dimensionsa = 8.879(2) Å α = 71.29(3)◦

b = 12.643(3) Å β = 80.79(3)◦

c = 15.062(3) Å γ = 78.58(3)◦

a = 17.1322(10) Å α = 90◦

b = 12.7920(5) Å β = 94.461(4)◦

c = 14.6083(7) Å γ = 90◦

Volume (Å3) 1561.2(7) 3191.8(3)Z 2 4

Calculated density (Mg m−3) 2.337 1.697Absorption coefficient (mm−1) 11.345 5.742

F(000) 1028 1616Crystal size (mm) 0.15 × 0.14 × 0.13 0.17 × 0.13 × 0.11

Theta range for data collection (◦) 2.55 to 29.278 3.219 to 29.509

Limiting indices−12 ≤ h ≤ 12−17 ≤ k ≤ 17−20 ≤ l ≤ 20

−20 ≤ h ≤ 23−16 ≤ k ≤ 17−20 ≤ l ≤ 20

Reflections collected/unique 24,229/8402 [Rint = 0.0747] 19,630/8551 [Rint = 0.0520]Completeness to theta (%) 99.9 98.8

Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 8402/0/481 8551/2/377Goodness-of-fit on F2 1.066 1.05

Final R indices [I > 2σ(I)] R1 = 0.0718, wR2 = 0.1867 R1 = 0.0631, wR2 = 0.1629R indices (all data) R1 = 0.1077, wR2 = 0.2158 R1 = 0.0880, wR2 = 0.1827

Largest diff. peak and hole (e Å−3) 3.404 and −4.129 2.368 and −2.488

Int. J. Mol. Sci. 2020, 21, 8696 19 of 26

3.5. Topological Analysis

Topological analysis of the metal-organic network of coordination polymers obtained wasperformed with the ToposPro program package [88] and the TTD collection of periodic networktopologies following the concept of the simplified underlying net. Such a net was generated bycontracting organic ligands to their centroids, maintaining their connectivity via coordination bondsand including secondary bonds. The underlying networks obtained have been topologically analyzedand classified [89,90].

3.6. DFT Calculations

Quantum-chemical calculations were performed in the framework of density-functional theory(DFT). Hybrid three-parameter Becke Lee-Yang-Parr functional B3LYP [91] together with Ahlrichs’triple-zeta split-valence basis set was augmented by Coulomb fitting (def2-TZVP) [92] usingresolution of the identity approximation [93]. The Stuttgart-Dresden effective core potential (ECP)for 60 core electrons of Bi was used [94]. The ORCA ab initio, DFT and semiempirical SCF-MOpackage [95] was used for all calculations. Truncated parts of [Bi2(2,3pydc)6 (2,3pydcH)2(H2O)]8−

(1) and [Bi(2,3pydc)2(2,3pydcH)Cl2]4− (2) were used as models for the DFT calculations. The modelof 1 appeared too large for calculations, so the ligands were truncated, keeping the positions ofN,O-donor atoms and some of non-coordinative organic fragments unchanged in comparisonto the initial structure. In the final case, the fragment of [Bi2(AcO)4(H2O)(CH2NCH2COO)(CH3NC(CH3)COO)2(CH3NCHCOO)] for 1 was included in the calculations. The positions ofhydrogen atoms were optimized, while other atoms retained the same coordinates as determined fromsingle-crystal X-ray analysis (cif files). Molecular orbitals were localized for analysis using Foster-Boys(spatial localization) algorithm [96]. Electron density distributions were visualized with the UCSFChimera package [97].

3.7. Solid-State Photoluminescence Measurements

The solid-state photoluminescence spectra were recorded at room temperature on aspectrofluorophotometer RF-5301 equipped with a 150 W Xenon lamp and a solid sample holder(Shimadzu, Kioto, Japan). The 3D emission spectra and 2D excitation and emission spectra werecollected with a 1.5 nm slit width for excitation and a 3 nm slit width for emission monochromators.Photoluminescence data were processed using Panorama (LabCognition GMBH, Cologne, Germany)software. Photoluminescence quantum yield was measured on a FLS980 spectrofluorimeter (EdinburghInstruments, Livingston, UK), equipped with an integrating sphere, using BaSO4 as a reference.

3.8. Solubility and Stability Studies

Solubility studies were performed using H2O, 1M HCl and commonly used organic solvents:MeOH, EtOH, iPrOH, MeCN, DMF, DMSO, Me2CO, THF and CH2Cl2. UV-Vis stability measurementswere conducted on a V-630 Jasco UV-Vis spectrophotometer (Jasco Corporation, Tokyo, Japan) using1 cm cuvettes. Analyzed compounds (ligand 2,3pydcH2, complexes 1 and 2) were dissolved in DMSOand diluted with H2O or 1M HCl 1:50 (v/v) to give concentration of 10−4 M. All the time-dependent(0 h, 24 h and 48 h) measurements were recorded at room temperature. The UV-Vis spectrum ofproduct of the reaction BiCl3 with H2O was measured in 1M HCl with an addition of 2% v/v DMSO ata concentration of 10−4 M at room temperature.

3.9. Bacterial Strains and Culture Conditions

Two Helicobacter pylori strains, 26695 [98] and N6 [99], were used to determine the MinimumInhibitory Concentration (MIC) of the synthesized Bi-compounds by agar dilution. H. pylori 26695 andN6 strains were cultured on Columbia Blood Agar Base plates (CBA, CM331, Oxoid, Basingstoke, UK)supplemented with 10% (v/v) defibrinated horse blood. Liquid cultures were grown with shaking at

Int. J. Mol. Sci. 2020, 21, 8696 20 of 26

140 rpm in BBL Brucella Broth (BBL, 211088, Beckton Dickinson, Franklin Lakes, NJ, USA) with 10%foetal calf serum (Biowest S1810). Liquid and solid H. pylori cultures were supplemented with 0.2%(v/v) mixture of antibiotics containing 0.3 mg L−1 polymyxin B, 12.5 mg L−1 vancomycin, 2.5 mg L−1

amphotericin B and 6.25 mg L−1 trimethoprim [100]. H. pylori were cultivated under microaerobicconditions (5% O2, 10% CO2, 85% N2) at 37 ◦C.

3.10. Determination of The Minimum Inhibitory Concentration (MIC)

The MIC values of bismuth(III) complexes (1 and 2), ligand (pyridine-2,3-dicarboxylic acid) andbismuth subsalicylate (BSS, Sigma-Aldrich, Steinheim, Germany) as a reference were determined bythe agar dilution technique. All compounds were dissolved in DMSO and mixed with CBA to give thedesired concentrations of the tested compounds. In the initial screening, concentrations ranging from 1to 100 µg mL−1 at intervals of 20 µg mL−1 were used. In the final analyses, the bismuth compoundconcentrations were used at intervals of 2.5 µg mL−1. H. pylori liquid cultures of OD600 ~0.5–1.5(log-phase, OD600 = 1 corresponds to ~6.5 × 108 CFU mL−1) were diluted in BBL to ~105 CFU mL−1.Aliquots (100 µL) of bacterial suspensions were then streaked onto previously prepared CBA platescontaining the different concentrations of tested compounds. CBA plates with DMSO at the sameconcentration as in CBA plates with compounds, or without DMSO, were used as controls of H. pylorigrowth under experimental conditions. The plates were incubated for 5 days, and then H. pylori growthwas assessed. The lowest concentration of a compound at which no H. pylori growth was observedwas considered as MIC.

4. Conclusions

In summary, we synthesized and fully physicochemically characterized two novel bismuth(III)coordination polymers, with pyridine-2,3-dicarboxylic acid (2,3pydcH2) as the prolinker. The molecularstructures of the obtained coordination polymers [Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1) and{(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2) indicated that the coordination environments of the metalcenters were different, mainly due to the influence of a free electron pair. The crystallographic studiesand quantum-chemical calculations pointed to a hemidirected geometry of bismuth centers in 1and a holodirected geometry in 2. The various coordination modes of bridging carboxylate ligands(µ4-κ2N,O:κO′:κO′′:κ2O′′,O′′′ and µ5-κ2N,O:κO:κO′:κO′′:κ2O′′,O′′′ in 1 and µ-κ2N,O:κ2O′′,O′′′ in 2)were responsible for the formation of 1D chains with 4,5C10 and 2C1 topologies. Both coordinationpolymers exhibited blue-light photoluminescence with emission maxima at 452 nm and 463/471nm for 1 and 2, respectively. The photoluminescence quantum yield of compound 2 was 8.36%,which makes it a good candidate for more specific studies of Bi-based fluorescent materials. Additionally,the in vitro tests evaluating the bacteriostatic activity against Helicobacter pylori showed that Bi(III)coordination polymers had good antibacterial properties. The MIC values of 1 and 2 towardsreference strain 26695 reached values of 13.7 and 36.8 µM, respectively. It can be concludedthat differences in the structures of coordination polymers ([Bi2(2,3pydc)2(2,3pydcH)2(H2O)]n (1)and {(Et3NH)2[Bi(2,3pydc)(2,3pydcH)Cl2]}n (2)) influences the antibacterial activity. Additionally,the H. pylori strain N6 was slightly more sensitive to compound 1 (MIC = 11.4 µM) than strain 26,695.Therefore, more detailed research in this field should be conducted.

Supplementary Materials: Supplementary materials can be found at http://www.mdpi.com/1422-0067/21/22/8696/s1. Table S1. Selected bands of the most important bonds in the FT-IR spectra of pyridine-2,3-dicarboxylicacid and Bi(III) polymers 1 and 2 (cm−1). Figure S1. The UV-Vis spectrum of the product of the reaction of BiCl3with H2O in 1M HCl solution.

Author Contributions: Conceptualization, I.Ł., M.K., J.M. and B.B.; methodology, formal analysis, M.K., J.M.;investigation, M.K., J.M., K.K., O.V.K., A.Z.-P., P.S.; writing—original draft preparation M.K., I.Ł., J.M. and B.B.;writing—review and editing, I.Ł., M.K.; visualization, M.K.; supervision, I.Ł., B.B. All authors have read andagreed to the published version of the manuscript.

http://www.mdpi.com/1422-0067/21/22/8696/s1

http://www.mdpi.com/1422-0067/21/22/8696/s1

Int. J. Mol. Sci. 2020, 21, 8696 21 of 26

Funding: Publication costs were supported by the Nicolaus Copernicus University in Torun (ExcellenceInitiative—Research University). Financial support from the statutory activity of subsidy from the PolishMinistry of Science and Higher Education for the Institute of Chemistry of the Jan Kochanowski University inKielce is gratefully acknowledged (SMGR.RN.20.259).

Acknowledgments: We would like to acknowledge the help and support of Bogumiła Kupcewicz during thephotoluminescence experiments.

Conflicts of Interest: The authors declare no conflict of interest.

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